Pam4 receiver including adaptive continuous-time linear equalizer and method of adaptively training the same using training data patterns

ABSTRACT

A PAM4 receiver including an adaptive continuous-time linear equalizer and a method for training the same are disclosed. The PAM4 receiver and the method for training the same of the present invention employs a training pattern including a first training data pattern and second training data pattern to adaptively tune the PAM4 receiver to achieve accurate data reception and long-distance, high-speed communication.

This non-provisional U.S. patent application claims priority under 35 U.S.C. § 119 of Korean Patent Applications No. 10-2020-0111959 filed on Sep. 2, 2020 and No. 10-2020-0133208 filed on Oct. 15, 2020, in the Korean Intellectual Property Office, the entire contents of which are hereby incorporated by reference.

1. Field

The present invention relates to a PAM4 receiver including an adaptive continuous-time linear equalizer and a method for training the same, and more particularly, a PAM4 receiver including an adaptive continuous-time linear equalizer and a method for adaptively training the same using training patterns.

2. Description of the Related Art

Various methods are used in order to transmit digital signals at high speed. While binary data are transmitted conventionally, multi-level pulse amplitude modulation (PAM) has been proposed to transmit digital data at high speed.

FIG. 1A through FIG. 1C are diagrams illustrating waveforms of binary PAM (PAM2) and multi-level PAM (PAM4, PAM8) signals, respectively.

FIG. 1A illustrates binary data having values ‘0’ and ‘1 ’. That is, in FIG. 1A, a two-level PAM (PAM2) signal is illustrated. While PAM2 signal is robust to noise, PAM2 has a limitation in increasing the data rate.

In order to overcome the limitation of PAM2, PAM4 and PAM8 have been proposed.

As shown in FIG. 1B, in PAM4, data having values of ‘00’, ‘01’, ‘10’ and ‘11’ are modulated into a signal with four data levels.

Similarly, as shown in FIG. 1C, in PAM8, data having values of ‘000’, ‘001’, ‘010’, ‘011’, ‘100’, ‘101’, ‘110’ and ‘111’ are modulated into a signal with eight data levels.

As a result, in PAM4 and PAM8, data may be transmitted at two and three times faster when compared to PAM2, respectively. However, PAM4 and PAM8 are more susceptible to attenuation and noise when compared to PAM2. Therefore, an equalizer for equalizing the received signal is needed in PAM4 and PAM8.

FIG. 2 is a block diagram illustrating a conventional PAM4 receiver.

Referring to FIG. 2, the conventional PAM4 receiver 100 includes a continuous-time linear equalizer (CTLE) 110, a sampler 120, a demultiplexer (DEMUX) 130 and a clock-and-data recovery (CDR) 140.

The CTLE 110 equalizes the received signal.

FIG. 3 is a circuit diagram illustrating the CTLE 110 shown in FIG. 2 in detail.

Referring to FIG. 3, the CTLE 110 is basically a differential amplifier circuit, and includes a capacitor C_(s) and a resistor R_(s) connected in parallel between the sources of the transistors.

The amplification gain of the high frequency component of the received signal is determined by the capacitance of the capacitor C_(s), and the amplification gain of the low frequency component of the received signal is determined by the resistance of the resistor R_(s).

The capacitance of the capacitor C_(s) and the resistance of the resistor R_(s) may be selected according to the degree of attenuation of the received signal.

FIG. 4 is a diagram illustrating a waveform of a signal CTLE_out according to the capacitance of the capacitor C_(s) and the resistance of the resistor R_(s).

Referring to FIG. 4, when the transmitted data “00”, “00”, “11”, “11”, “11”, “11”, “00”, “00” are not equalized (meaning C_(s)=0)after receiving the same, a signal CTLE_out having a waveform denoted as (i) in FIG. 4 is obtained due to the attenuation of the high frequency component.

When only the capacitance of the capacitor C_(s) is increased (“normal C_(s)”) with respect to (i) in FIG. 4, a signal CTLE_out having a waveform denoted as (ii) in FIG. 4 is obtained with an increase in the high frequency component.

When only the capacitance of the capacitor C_(s) is further increased (“large C_(s)”) with respect to (ii) in FIG. 4, a signal CTLE_out having a waveform denoted as (iii) in FIG. 4 is obtained with a more increase in the high frequency (HF) component.

When the resistance of the resistor R_(s) is increased (“large R_(s)”) with respect to (iii) in FIG. 4, a signal CTLE_out having a waveform denoted as (iv) in FIG. 4 is obtained with a decrease in the low frequency (LF) component. The signal CTLE_out denoted as (iii) in FIG. 4 is shown in dotted line for comparison.

When the resistance of the resistor R_(s) is decreased (“small R_(s)”) with respect to (iii) in FIG. 4, a signal CTLE_out having a waveform denoted as (v) in FIG. 4 is obtained with an increase in the low frequency component. The signal CTLE_out denoted as (iii) in FIG. 4 is shown in dotted line for comparison.

Here, (ii) in FIG. 4 represents under equalization, and (iii), (iv) and (v) in FIG. 4 represent over-equalizations. As shown, the high frequency component increases by equalization as the capacitance of the capacitor C_(s) increases, and the low frequency component decreases by equalization as the resistance of the resistor R_(s) increases.

The sampler 120 samples the output signal CTLE_out of the CTLE 110.

The sampler 120 may be embodied by the circuit exemplified in FIG. 5.

FIG. 5 illustrates an example sampler used in PAM4 receiver.

As shown in FIG. 5, the signal CTLE_out is inputted to the three adders 124-1, 124-2 and 124-3, and the adders 124-1, 124-2 and 124-3 outputs the difference between: the signal CTLE_out; and the threshold voltages V_(TH01), V_(TH12) and V_(TH23), respectively.

The difference between the signal CTLE_out and the threshold voltage V_(TH01) is inputted to flip-flops 121-1, 121-2, 121-3 and 121-4, the difference between the signal CTLE_out and the threshold voltage V_(TH12) is inputted to flip-flops (122-1, 122-2, 122-3 and 122-4, and the difference between the signal CTLE_out and the threshold voltage V_(TH23) is inputted to flip-flops 123-1, 123-2, 123-3 and 123-4.

The flip-flops 121-1, 121-2, 121-3 and 121-4 sample the difference between the signal CTLE_out and the threshold voltage V_(TH01) at the rising edges of the clock signals DCK, DCKB, XCK and XCKB, respectively and output the sampled values as signals DET[0], DOT[0], XET[0] and XOT[10], respectively.

The flip-flops 122-1, 122-2, 122-3 and 122-4 sample the difference between the signal CTLE_out and the threshold voltage V_(TH12) at the rising edges of the clock signals DCK, DCKB, XCK and XCKB, respectively and output the sampled values as signals DET[1], DOT[1], XET[1] and XOT[2], respectively.

The flip-flops 123-1, 123-2, 123-3 and 123-4 sample the difference between the signal CTLE_out and the threshold voltage V_(TH23) at the rising edges of the clock signals DCK, DCKB, XCK and XCKB, respectively and output the sampled values as signals DET[2], DOT[2], XET[2] and XOT[2], respectively.

FIG. 6 is a waveform diagram illustrating signals in the conventional PAM4 receiver, wherein an example “transmitted data”, the signal CTLE_out outputted by the PAM4 receiver corresponding to the received “transmitted data”, and the clock signals DCK, DCKB, XCK and XCKB for sampling the signal CTLE_out are shown.

Referring to FIG. 6, while “transmitted data” is a PAM4 signal without distortion, the received signal contains distortion due to the attenuation of a high frequency component occurring during transmission. As a result, the received signal may not be regarded as an unimpaired PAM4 signal. Therefore, the received signal requires equalization by the CTLE 110 shown in FIG. 2. The signal equalized by the CTLE 110 is outputted as the signal CTLE_out and then inputted to the sampler 120. As shown in FIG. 6, the signal CTLE_out is a signal having the high frequency component of the received signal compensated.

Here, the data level of value “00” is denoted as dlev₀, the data level of value “01” is denoted as dlev₁, the data level of value “10” is denoted as dlev₂, and the data level of value “11” is denoted as dlev₃. The threshold voltage V_(TH01) is the average value of the data level dlev₀ and the data level dlev₁, the threshold voltage V_(TH12) is the average value of the data level dlev₁ and the data level dlev₂, and the threshold voltage V_(TH23) is the average value of the data level dlev₂ and data level dlev₃.

The sampler 120 samples the signal CTLE_out according to the clock signals DCK, DCKB, XCK and XCKB shown in FIG. 6.

Referring to FIG. 6, the clock signal DCK is a clock signal for sampling the signal CTLE_out at the center of the symbol, and the clock signal DCKB is an inverted signal of the clock signal DCK with one half period difference between the rising edges of the clock signals DCKB and DCK for sampling the signal CTLE_out at the center of the symbol similar to the clock signal DCK. The signal CTLE_out is sampled once in each period alternately according to the clock signals DCK and DCKB.

On the other hand, the clock signal XCK is a clock signal for sampling the signal CTLE_out at the transition section thereof, and the clock signal XCKB is an inverted signal of the clock signal XCK with one half period difference between the rising edges of the clock signals XCKB and XCK for sampling the signal CTLE_out at the transition section thereof similar to the clock signal XCK. The transition section of the signal CTLE_out is sampled once in each period alternately according to the clock signals XCK and XCKB.

Referring back to FIG. 5, when the signal CTLE_out is sampled according to the clock signals DCK, DCKB, XCK and XCKB, signals DET[2:0], DOT[2:0], XET[2:0] and XOT[2:0] are obtained.

In the clock signals DCK, DCKB, XCK and XCKB, ‘D’ signifies clock signal for sampling at the center of the symbol of the signal CTLE_out, and ‘X’ signifies clock signal for sampling at the transition section of the signal CTLE_out. In the signals DET[2:0], DOT[2:0], XET[2:0] and XOT[2:0], ‘D’ signifies data obtained by sampling at the center of the symbol of the signal CTLE_out, ‘X’ signifies data obtained by sampling at the transition section of the signal CTLE_out, ‘E’ signifies the even-numbered data, and ‘O’ signifies the odd-numbered data. In addition, ‘T’ signifies that the signals DET[2:0], DOT[2:0], XET[2:0], XOT[2:0] are thermometer codes as shown in Table 1 below.

TABLE 1 data level of CTLE_out Signals DET[2:0], DOT[2:0], XET[2:0] (binary code) and XOT[2:0] (thermometer code) “00” “000” “01” “001” “10” “011” “11” “111”

The signal DET[2:0] and DOT[2:0] indicate where the voltage level of the signal CTLE_out falls among the PAM4 data levels. The signal XET[2:0] and XOT[2:0] indicate the data levels of the transition section sampled according to the clock signal XCK and XCKB.

The DEMUX 130 parallelizes the output signal of the sampler 120 and outputs the parallelized output signal of the sampler 120 as the signal DATA_out.

Specifically, the DEMUX 130 parallelizes the signals DET[2:0], DOT[2:0], XET[2:0], XOT[2:0] according to a predetermined clock signal, and outputs the parallelized output signal of the sampler 120 as the signal DATA_out. More specifically, since the signals DET[2:0], DOT[2:0], XET[2:0] and XOT[2:0] are not simultaneously outputted, the signals DET[2:0], DOT[2:0], XET[2:0] and XOT[2:0] are parallelized (synchronized) according to the predetermined clock signal and outputted as the signal DATA_out.

In addition, the DEMUX 130 provides the signal DATA_out to the CDR 140.

The CDR (Clock-and-Data Recovery) 140 provides the sampling clock signal DCK, XCK, DCKB and XCKB to the sampler 120.

Specifically, the CDR 140 adjusts timing or phase of the sampling clock signals DCK, XCK, DCKB and XCKB according to the signals DET[2:0], DOT[2:0], XET[2:0] and XOT[2:0].

While the conventional PAM4 receiver is capable of equalization by adjusting R_(s) and C_(s), the equalization cannot be performed adaptively, resulting in being unable to perform equalization according to received data.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a PAM4 receiver including an adaptive continuous-time linear equalizer and a method for adaptively training the same using training patterns.

According to one aspect of the present invention, there is provided a PAM4 receiver comprising: a linear equalizer receiving a signal containing: (i) a first training data pattern containing data “00” and consecutively arranged first data “11” through m^(th data “)11”; and (ii) a second training data pattern including one of data “01”, data “10” and combinations thereof, and equalizing the signal according to an equalization parameter of the linear equalizer including a high frequency amplification gain and a low frequency amplification gain, and outputting a signal CTLE_out containing equalized first training data pattern and equalized second training data pattern; a sampler sampling: (i) a difference dlev_(3HD); (ii) a difference dlev_(3LD); and (iii) a difference dlev_(1D) or dlev_(2D), and outputting sampled differences as a signal SAMPLE_out, wherein the difference dlev_(3HD) is a difference between: a first voltage level of the signal CTLE_out corresponding to the first data “11” of the equalized first training data pattern when a transition from the data “00” to the first data “11” occurs; and an upper limit dlev_(3H), the difference dlev_(3LD) is a difference between: a second voltage level of the signal CTLE_out corresponding to one of second data “11” through the m^(th) data “11” of the equalized first training data pattern; and a lower limit dlev_(3L), the difference dlev_(1D) is a difference between: a third voltage level of the signal CTLE_out corresponding to the data “01” of the equalized second training data pattern; and the data level dlev₁, corresponding to the data “01”, and the difference dlev_(2D) is a difference between: a fourth voltage level of the signal CTLE_out corresponding to the data “10” of the equalized second training data pattern; and the data level dlev₂ corresponding to data “10”; a DEMUX parallelizing the signal SAMPLE_out, and outputting parallelized signal SAMPLE_out as a signal DATA_out; a CDR providing a clock signal for sampling to the sampler and the DEMUX; and a controller: (i) adaptively adjusting a high frequency amplification gain and a low frequency amplification gain of the linear equalizer by generating and providing a signal EQ_AC[N_(AC)-1:0] and a signal EQ_DC[N_(DC)-1:0] for adjusting the high frequency amplification gain and low frequency amplification gain based on the difference dlev_(3HD) and the difference dlev_(3LD) in the signal DATA_out, respectively; and (ii) providing the sampler with threshold voltages V_(TH01), V_(TH12) and V_(TH23), the data level dlev₁ or dlev₂, and the upper limit dlev_(3H) and the lower limit dlev_(3L), wherein the threshold voltages V_(TH01), V_(TH12) and V_(TH23) are calculated from: a data level dlev₀ corresponding to the data “00”; the data level dlev₁ or dlev₂; and a data level dlev₃ corresponding to the data “11”, the data levels dlev₁ and dlev₂ are determined from the differences dlev_(1D) and dlev_(2D), respectively; and the data level dlev₃ is determined from the upper limit dlev_(3H) and the lower limit dlev_(3L) (where m is a natural number equal to or greater than 2, and N_(AC) and N_(DC) are natural numbers, respectively).

Preferably, the linear equalizer comprises: a differential amplifier provided with transistors; N_(AC) capacitors C_(unit) connected between sources of the transistors; and N_(DC) resistors R_(unit) connected between the sources of the transistors, and the controller selectively turns on the N_(AC) capacitors C_(unit) according to the signal EQ_AC[N_(AC)-1:0] to adaptively adjust the high frequency amplification gain, and selectively turns on the N_(DC) resistor R_(unit) according to the signal EQ_DC[N_(DC)-1:0] to adaptively adjust the low frequency amplification gain.

Preferably, the controller lowers the upper limit dlev_(3H) and the lower limit dlev_(3L) when the first voltage level of the signal CTLE_out is lower than the upper limit dlev_(3H) even with the high frequency amplification gain at maximum by turning on an entirety of the N_(AC) capacitors C_(unit).

Preferably, the controller: determines the data level dlev₁ or dlev₂ based on a sign of the difference dlev_(1D) or dlev_(2D); and provides the sampler with the threshold voltages V_(TH01), V_(TH12) and V_(TH23) thereof calculated according to equations

${{dlev}_{3} = \frac{{dlev_{3H}} + {dlev_{3L}}}{2}},{V_{TH01} = \frac{{dlev_{0}} + {dlev}_{1}}{2}},{V_{TH12} = {{\frac{{dlev_{1}} + {dlev_{2}}}{2}\mspace{14mu}{and}\mspace{14mu} V_{TH23}} = {\frac{{dlev_{2}} + {dlev}_{3}}{2}.}}}$

According to another aspect of the present invention, there is provided a PAM4 receiver comprising: a linear equalizer receiving a signal containing: (i) a first training data pattern containing data “11” and consecutively arranged first data “00” through m^(th) data “00”; and (ii) a second training data pattern including one of data “01”, data “10” and combinations thereof, and equalizing the signal according to an equalization parameter of the linear equalizer including a high frequency amplification gain and a low frequency amplification gain, and outputting a signal CTLE_out containing equalized first training data pattern and equalized second training data pattern; a sampler sampling: (i) a difference dlev_(0LD); (ii) a difference dlev_(0HD); and (iii) a difference dlev_(1D) or dlev_(2D), and outputting sampled differences as a signal SAMPLE_out, wherein the difference dlev_(0LD) is a difference between: a first voltage level of the signal CTLE_out corresponding to the first data “00” of the equalized first training data pattern when a transition from the data “11” to the first data “00” occurs; and a lower limit dlev_(0L), the difference dlev_(0HD) is a difference between: a second voltage level of the signal CTLE_out corresponding to one of second data “00” through the m^(th) data “00” of the equalized first training data pattern; and an upper limit dlev_(0H), the difference dlev_(2D) is a difference between: a third voltage level of the signal CTLE_out corresponding to the data “10” of the equalized second training data pattern; and the data level dlev₂ corresponding to the data “10”, and the difference dlev_(1D) is a difference between: a fourth voltage level of the signal CTLE_out corresponding to the data “01” of the equalized second training data pattern; and the data level dlev₁ corresponding to data “01”; a DEMUX parallelizing the signal SAMPLE_out, and outputting parallelized signal SAMPLE_out as a signal DATA_out; a CDR providing a clock signal for sampling to the sampler and the DEMUX; and a controller: (i) adaptively adjusting a high frequency amplification gain and a low frequency amplification gain of the linear equalizer by generating and providing a signal EQ_AC[N_(AC)-1:0] and a signal EQ_DC[N_(DC)-1:0] for adjusting the high frequency amplification gain and low frequency amplification gain based on the difference dlev_(0LD) and the difference dlev_(0HD) in the signal DATA_out, respectively; and (ii) providing the sampler with threshold voltages W_(TH01), V_(TH12) and V_(TH23), the data level dlev₁ or dlev₂, and the upper limit dlev_(0H) and the lower limit dlev_(0L), wherein the threshold voltages V_(TH01), V_(TH12) and V_(TH23) are calculated from: a data level dlev₀ corresponding to the data “00”; the data level dlev₁ or dlev₂; and a data level dlev₃ corresponding to the data “11”, the data levels dlev₁ and dlev₂ are determined from the differences dlev_(1D) and dlev_(2D), respectively; and the data level dlev₀ is determined from the lower limit dlev_(0L) and the upper limit dlev_(0H) (where m is a natural number equal to or greater than 2, and N_(AC) and N_(DC) are natural numbers, respectively).

Preferably, the linear equalizer comprises: a differential amplifier provided with transistors; N_(AC) capacitors C_(unit) connected between sources of the transistors; and N_(DC) resistors R_(unit) connected between the sources of the transistors, and the controller selectively turns on the N_(AC) capacitors C_(unit) according to the signal EQ_AC[N_(AC)-1:0] to adaptively adjust the high frequency amplification gain, and selectively turns on the N_(DC) resistor R_(unit) according to the signal EQ_DC[N_(DC)-1:0] to adaptively adjust the low frequency amplification gain.

Preferably, the controller elevates the upper limit dlev_(0H) and the lower limit dlev_(0L) when the first voltage level of the signal CTLE_out is higher than the lower limit dlev_(0L) even with the high frequency amplification gain at maximum by turning on an entirety of the N_(AC) capacitors C_(unit).

Preferably, the controller: determines the data level dlev₁ or dlev₂ based on a sign of the difference dlev_(1D) or dlev_(2D); and provides the sampler with the threshold voltages V_(TH01), V_(TH12) and V_(TH23) thereof calculated according to equations

${{dlev}_{0} = \frac{{dlev_{0H}} + {dlev_{0L}}}{2}},{V_{TH01} = \frac{{dlev_{0}} + {dlev}_{1}}{2}},{V_{TH12} = {{\frac{{dlev_{1}} + {dlev_{2}}}{2}\mspace{14mu}{and}\mspace{14mu} V_{TH23}} = {\frac{{dlev_{2}} + {dlev}_{3}}{2}.}}}$

According to yet another aspect of the present invention, there is provided a method of training a PAM4 receiver comprising a linear equalizer, a sampler, a DEMUX and a controller, the method comprising: (a) receiving a signal containing: (i) a first training data pattern containing data “00” and consecutively arranged first data “11” through m^(th) data “11”; and (ii) a second training data pattern including one of data “01”, data “10” and combinations thereof; (b) equalizing the signal received in step (a) according to an equalization parameter of the linear equalizer including a high frequency amplification gain and a low frequency amplification gain, and outputting a signal CTLE_out containing equalized first training data pattern and equalized second training data pattern; (c) sampling: (i) a difference dlev_(3HD); (ii) a difference dlev_(3LD); and (iii) a difference dlev_(1D) or dlev_(2D) according to a sampling parameter of the sampler, and outputting sampled differences as a signal SAMPLE-out, wherein the difference dlev_(3HD) is a difference between: a first voltage level of the signal CTLE_out corresponding to the first data “11” of the equalized first training data pattern when a transition from the data “00” to the first data “11” occurs; and an upper limit dlev_(3H), the difference dlev_(3LD) is a difference between: a second voltage level of the signal CTLE_out corresponding to one of second data “11” through the m^(th) data “11” of the equalized first training data pattern; and a lower limit dlev_(3L), the difference dlev_(1D) is a difference between: a third voltage level of the signal CTLE_out corresponding to the data “01” of the equalized second training data pattern; and the data level dlev₁ corresponding to the data “01”, and the difference dlev_(2D) is a difference between: a fourth voltage level of the signal CTLE_out corresponding to the data “10” of the equalized second training data pattern; and the data level dlev₂ corresponding to data “10”; (d) parallelizing the signal SAMPLE_out, and outputting parallelized signal SAMPLE_out as a signal DATA_out; (e) generating a signal EQ_AC[N_(AC)-1:0] and a signal EQ_DC[N_(DC)-1:0] for adjusting the high frequency amplification gain and low frequency amplification gain based on the difference dlev_(3HD) and the difference dlev_(3LD) in the signal DATA_out, respectively; (f) generating threshold voltages V_(TH01), V_(TH12) and V_(TH23) of the sampler by calculating the threshold voltages V_(TH01), V_(TH12) and V_(TH23) from: a data level dlev₀ corresponding to the data “00”; the data level dlev₁ or dlev₂; and a data level dlev₃ corresponding to the data “11”, wherein the data level dlev₁ or dlev₂ is determined from the difference dlev_(1D) or dlev_(2D), respectively, and the data level dlev₃ is determined from the upper limit dlev_(3H) and the lower limit dlev_(3L); (g) adaptively adjusting the equalization parameter including the high frequency amplification gain and low frequency amplification using the signal EQ_AC[N_(AC)-1:0] and signal EQ_DC[N_(DC)-1:0] generated in step (e); and (h) adaptively adjusting the sampling parameter of the sampler according to the threshold voltages V_(TH01), V_(TH12) and V_(TH23), the data level dlev₁ or dlev₂, and the upper limit dlev_(3H) and the lower limit dlev_(3L) generated in step (f) (where m is a natural number equal to or greater than 2, and N_(AC) and N_(DC) are natural numbers, respectively).

Preferably, the method further comprises: performing step (a) through step (d) after performing step (a) through step (h) based on the equalization parameter and the sampling parameter adaptively adjusted in step (g) and step (h), respectively.

Preferably, step (f) comprises: (f-1) determining the data level dlev₁ or dlev₂ based on a sign of the difference dlev_(1D) or dlev_(2D); and (f-2) calculating the threshold voltages V_(TH09), V_(TH12) and V_(TH23) according to equations

${dlev}_{3} = \frac{{dlev_{3H}} + {dlev_{3L}}}{2}$ ${V_{TH01} = \frac{{dlev_{0}} + {dlev}_{1}}{2}},{V_{TH12} = {\frac{{dlev_{1}} + {dlev_{2}}}{2}\mspace{14mu}{and}}}$ $V_{TH23} = {\frac{{dlev_{2}} + {dlev}_{3}}{2}.}$

Preferably, step (g) comprises: (g-1) selectively turning on N_(AC) capacitors C_(unit) provided in the linear equalizer according to the signal EQ_AC[N_(AC)-1:0] to adaptively adjust the high frequency amplification gain; and (g-2) selectively turning on N_(DC) resistor R_(unit) provided in the linear equalizer according to the signal EQ_DC[N_(DC)-1:0] to adaptively adjust the low frequency amplification gain.

Preferably, step (g) further comprises: (g-3) lowering the upper limit dlev_(3H) and the lower limit dlev_(3L) when the first voltage level of the signal CTLE_out is lower than the upper limit dlev_(3H) even with the high frequency amplification gain at maximum by turning on an entirety of the N_(AC) capacitors C_(unit).

According to yet another aspect of the present invention, there is provided a method of training a PAM4 receiver comprising a linear equalizer, a sampler, a DEMUX and a controller, the method comprising: (a) receiving a signal containing: (i) a first training data pattern containing data “11” and consecutively arranged first data “00” through m^(th) data “00”; and (ii) a second training data pattern including one of data “01”, data “10” and combinations thereof; (b) equalizing the signal received in step (a) according to an equalization parameter of the linear equalizer including a high frequency amplification gain and a low frequency amplification gain, and outputting a signal CTLE_out containing equalized first training data pattern and equalized second training data pattern; (c) sampling: (i) a difference dlev_(0LD); (ii) a difference dlev_(0HD); and (iii) a difference dlev_(1D) or dlev_(2D) according to a sampling parameter of the sampler, and outputting sampled differences as a signal SAMPLE_out, wherein the difference dlev_(0LD) is a difference between: a first voltage level of the signal CTLE_out corresponding to the first data “00” of the equalized first training data pattern when a transition from the data “11” to the first data “00” occurs; and a lower limit dlev_(0L), the difference dlev_(0HD) is a difference between: a second voltage level of the signal CTLE_out corresponding to one of second data “00” through the m^(th) data “00” of the equalized first training data pattern; and an upper limit dlev_(0H), the difference dlev_(2D) is a difference between: a third voltage level of the signal CTLE_out corresponding to the data “10” of the equalized second training data pattern; and the data level dlev₂ corresponding to the data “10”, and the difference dlev_(1D) is a difference between: a fourth voltage level of the signal CTLE_out corresponding to the data “01” of the equalized second training data pattern; and the data level dlev₁ corresponding to data “01”; (d) parallelizing the signal SAMPLE_out, and outputting parallelized signal SAMPLE_out as a signal DATA_out; (e) generating a signal EQ_AC[N_(AC)-1:0] and a signal EQ_DC[N_(DC)-1:0] for adjusting the high frequency amplification gain and low frequency amplification gain based on the difference dlev_(0LD) and the difference dlev_(0HD) in the signal DATA_out, respectively; (f) generating threshold voltages V_(TH01), V_(TH12) and V_(TH23) of the sampler by calculating the threshold voltages V_(TH01), V_(TH12) and V_(TH23) from: a data level dlev₀ corresponding to the data “00”; the data level dlev₁ or dlev₂; and a data level dlev₀ corresponding to the data “11”, wherein the data level dlev₁ or dlev₂ is determined from the difference dlev_(1D) or dlev_(2D), respectively, and the data level dlev₀ is determined from the lower limit dlev_(0L) and the upper limit dlev_(0H); (g) adaptively adjusting the equalization parameter including the high frequency amplification gain and low frequency amplification using the signal EQ_AC[N_(AC)-1:0] and signal EQ_DC[N_(DC)-1:0] generated in step (e); and (h) adaptively adjusting the sampling parameter of the sampler according to the threshold voltages V_(TH01), V_(TH12) and V_(TH23), the data level dlev₁ or dlev₂, and the lower limit dlev_(0L) and the upper limit dlev_(0H) generated in step (f) (where m is a natural number equal to or greater than ₂, and N_(AC) and N_(DC) are natural numbers, respectively).

Preferably, the method further comprises: performing step (a) through step (d) after performing step (a) through step (h) based on the equalization parameter and the sampling parameter adaptively adjusted in step (g) and step (h), respectively.

Preferably, step (f) comprises: (f-1) determining the data level dlev₁ or dlev₂ based on a sign of the difference dlev_(1D) or dlev_(2D), respectively, and (f-2) calculating the threshold voltages V_(TH01), V_(TH12) and V_(TH23) according to equations

${{dlev}_{0} = \frac{{dlev_{0H}} + {dlev_{0L}}}{2}},{V_{TH01} = \frac{{dlev_{0}} + {dlev}_{1}}{2}},{V_{TH12} = {{\frac{{dlev_{1}} + {dlev_{2}}}{2}\mspace{14mu}{and}\mspace{14mu} V_{TH23}} = {\frac{{dlev_{2}} + {dlev}_{3}}{2}.}}}$

Preferably, step (g) comprises: (g-1) selectively turning on N_(AC) capacitors C_(unit) provided in the linear equalizer according to the signal EQ_AC[N_(AC)-1:0] to adaptively adjust the high frequency amplification gain; and (g-2) selectively turning on N_(DC) resistor R_(unit) provided in the linear equalizer according to the signal EQ_DC[N_(DC)-1:0] to adaptively adjust the low frequency amplification gain.

Preferably, step (g) further comprises: (g-3) elevating the lower limit dlev_(0L) and the upper limit dlev_(0H) when the first voltage level of the signal CTLE_out is higher than the lower limit dlev_(0L) even with the high frequency amplification gain at maximum by turning on an entirety of the N_(AC) capacitors C_(unit).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A through FIG. 1C are diagrams illustrating binary PAM (PAM2), and multi-level PAM (PAM4, PAM8) signals, respectively.

FIG. 2 is a block diagram illustrating a conventional PAM4 receiver.

FIG. 3 is a circuit diagram illustrating, in detail, the CTLE 110 shown in FIG. 2.

FIG. 4 is a diagram illustrating a waveform of a signal CTLE_out according to the capacitance of the capacitor C_(s) and the resistance of the resistor R_(s).

FIG. 5 is a block diagram illustrating a sampler used in a conventional PAM4 receiver.

FIG. 6 is a waveform diagram illustrating signals in the conventional PAM4 receiver.

FIG. 7 is a block diagram illustrating a PAM4 receiver according to the present invention.

FIG. 8 is a circuit diagram illustrating, in detail, the CTLE of the PAM4 receiver shown in FIG. 7.

FIG. 9A through FIG. 9D are diagrams illustrating in detail the sampler of the PAM4 receiver shown in FIG. 7.

FIG. 10A and FIG. 10B are waveform diagrams for describing the operation of the PAM4 receivers according to first and second embodiments of the present invention, respectively.

FIG. 11A and FIG. 11B are flow diagrams illustrating methods of training the PAM4 receivers according to the first and the second embodiments of the present invention, respectively.

FIG. 12A and FIG. 12B are flow diagrams illustrating, in detail, step S150 and step S250 shown in FIG. 11A and FIG. 11B, respectively.

FIG. 13A and FIG. 13B are flow diagrams illustrating, in detail, step S160 and step S260 shown in FIG. 11A and FIG. 11B, respectively.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a PAM4 receiver including an adaptive continuous-time linear equalizer and a method for adaptively training the same using training patterns according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 7 is a block diagram illustrating a PAM4 receiver according to the present invention.

Referring to FIG. 7, a PAM4 receiver 1000 according to the present invention includes a continuous-time linear equalizer (CTLE) 1100, a sampler 1200, a DEMUX 1300, a clock-and-data recovery (CDR) 1400 and a controller 1500.

CTLE 1100 equalizes a received signal and outputs an equalized signal CTLE_out.

FIG. 8 is a circuit diagram illustrating, in detail, the CTLE of the PAM4 receiver 1000 shown in FIG. 7.

Referring to FIG. 8, the CTLE 1100 is basically a differential amplifier circuit, and includes a plurality (N_(AC)) of capacitors C_(unit) and a plurality (N_(DC)) of resistors R_(unit) connected in parallel to the sources of the transistors (where N_(AC) and N_(DC) are natural numbers, respectively).

The plurality of capacitors C_(unit) are selectively turned on or off by a signal EQ_AC[N_(AC)-1:0]. For example, when 8 capacitors C_(unit) are provided and the signal EQ_AC[7:0] has a value of “00001111”, 4 capacitors C_(unit) are turned on, and the remaining 4 capacitors C_(unit) are turned off.

The amplification gain of the high frequency component is determined according to the number of capacitors C_(unit) turned on by the signal EQ_AC[N_(AC)-1:0] among the plurality of capacitors C_(unit).

A plurality of resistors R_(unit) are selectively turned on or off by a signal EQ_DC[N_(DC)-1:0]. For example, when 8 resistors R_(unit) are provided and the signal EQ_DC[7:0] has a value of “00000111”, 3 resistors R_(unit) are turned, and the remaining 5 resistors R_(unit) are turned off.

The amplification gain of the low frequency component is determined according to the number of resistors R_(unit) turned on by the signal EQ_DC[N_(DC)-1:0] among the plurality of resistors R_(unit).

The signal EQ_AC[N_(AC)-1:0] and the signal EQ_DC[N_(DC)-1:0] are adaptively generated by the controller 1500.

FIG. 9A through FIG. 9D are diagrams illustrating, in detail, the sampler 1200 of the PAM4 receiver shown in FIG. 7 wherein the sampler 1200 samples the signal CTLE_out and outputs a signal SAMPLE_out which basically corresponds to the sampled CTLE_out.

FIG. 9A is a block diagram illustrating a sampler used in a training mode of the PAM4 receiver according to the present invention.

Referring to FIG. 9A, a sampler 1200 a for the training mode of the PAM4 receiver according to the present invention includes flip-flops 1210-1, 1210-2, 1220-1, 1220-2, 1220-3, 1220-4, 1230-1, 1230-2, 1240-1 and 1240-2 and adders 1250-1, 1250-2, 1250-3 and 1250-4.

The signal CTLE_out of the CTLE 1100 is inputted to the four adders 1250-1, 1250-2, 1250-3 and 1250-4, respectively, and the adder 1250-1 outputs a difference dlev_(1D) between the signal CTLE_out and a data level dlev₁, the adder 1250-2 outputs a difference V_(TH12D) between the signal CTLE_out and a threshold voltage V_(TH12), the adder 1250-3 outputs a difference dlev_(3LD) between the signal CTLE_out and a data level dlev_(3L), and the adder 1250-4 outputs a difference dlev_(3HD) between the signal CTLE_out and a data level dlev_(3H).

The difference dlev_(1D) between the signal CTLE_out and the data level dlev₁ is inputted to the flip-flops 1210-1 and 1210-2, and is sampled at the rising edges of the clock signals DCK and DCKB and outputted as signals AEd₁ and AOd₁ by the flip-flops 1210-1 and 1210-2, respectively. The difference V_(TH12D) between the signal CTLE_out and the threshold voltage V_(TH12) is inputted to the flip-flops 1220-1, 1220-2, 1220-3 and 1220-4, and is sampled at the rising edges of clock signals DCK, DCKB, XCK and XCKB and outputted as signals DET[1], DOT[1], XET[1] and XOT[1] by the flip-flops 1220-1, 1220-2, 1220-3 and 1220-4, respectively.

In addition, the difference dlev_(3LD) between the signal CTLE_out and the data level dlev_(3L) is inputted to the flip-flops 1230-1 and 1230-2, and is sampled at the rising edges of the clock signals DCK and DCKB and outputted as signals AEd_(3L) and AOd_(3L) by the flip-flops 1230-1 and 1230-2, respectively. The difference dlev_(3HD) between the signal CTLE_out and the data level dlev_(3H) is inputted to the flip-flops 1240-1 and 1240-2, is sampled at the rising edges of the clock signals DCK and DCKB and outputted as signals AEd_(3H) and AOd_(3H) by the flip-flops 1240-1 and 1240-2, respectively.

Here, the signals outputted by the flip-flops represent the sign of the signal inputted to the flip-flops. For example, when the value of the signal AEd_(3H) obtained by sampling the difference dlev_(3HD) is “1”, it indicates that the difference dlev_(3HD) is a positive number. In other words, it indicates that the voltage level of the signal CTLE_out is higher than that of the data level dlev_(3H). Similarly, when the value of signal AEd_(3H) is “0”, it indicates that the difference dlev_(3HD) is a negative number. That is, it indicates that the voltage level of the signal CTLE_out is smaller than that of the data level die V_(3H).

FIG. 9B is a block diagram illustrating a sampler which is a combination of the samplers shown in FIG. 9A and FIG. 5.

Referring to FIG. 9B, a sampler 1200 b of the PAM4 receiver according to the present invention differs from the sampler 120 shown in FIG. 5 in that the sampler 1200 b further includes the flip-flops 1240-1 and 1240-2 and the adder 1250-4 of the sampler 1200 a shown in FIG. 9A added to the sampler 120 shown in FIG. 5.

Additional difference between the sampler 1200 b shown in FIG. 9B and the sampler 120 shown in FIG. 5 is as follows.

First, the sampler 1200 b differs from the sampler 120 shown in FIG. 5 in that, in the training mode, the adder 1250-1 outputs the difference dlev_(1D) between the signal CTLE_out and the data level dlev₁, and the difference dlev_(1D) is sampled at the rising edges of the clock signals DCK, DCKB, XCK and XCKB and outputted as the signals AEd₁, AOd₁, XEd₁ and XOd₁ by the flip-flops 1210-1, 1210-2, 1210-3 and 1210-4, respectively. In addition, the sampler 1200 b differs from the sampler 120 shown in FIG. 5 in that, when the sampler 1200 b is actually in use after exiting the training mode, the adder 1250-1 outputs the difference V_(TH01D) between the signal CTLE_out and a threshold voltage V_(TH01), and the difference V_(TH01D) is sampled at the rising edges of clock signals DCK, DCKB, XCK and XCKB, and is outputted as the signals DET[0], DOT[0], XET[0] and XOT[0] by the flip-flops 1210-1, 1210-2, 1210-3 and 1210-4, respectively.

Similarly, the sampler 1200 b differs from the sampler 120 shown in FIG. 5 in that the adder 1250-3 and the flip-flops 1230-1, 1230-2, 1230-3 and 1230-4, as well as the adder 1250-1 and the flip-flops 1210-1, 1210-2, 1210-3 and 1210-4, sample and output the corresponding signal.

FIG. 9C is a block diagram illustrating another example of the sampler used in the training mode of the PAM4 receiver according to the present invention.

Referring to FIG. 9C, a sampler 1200 c used in the training mode of the PAM4 receiver according to the present invention includes flip-flops 1210-1, 1210-2, 1220-1, 1220-2, 1220-3, 1220-4, 1230-1, 1230-2, 1240-1 and 1240-2 and adders 1250-1, 1250-2, 1250-3 and 1250-4.

The sampler 1200 c shown in FIG. 9C has the same configuration as the sampler 1200 a shown in FIG. 9A. However, the signals inputted to the sampler 1200 c differ from those inputted to the sampler 1200 a.

Specifically, the sampler 1200 c differs from the sampler 1200 a in that data level dlev₂ is inputted to the adder 1250-1 instead of the data level dlev₁, and data levels dlev_(0H) and dlev_(0L) are inputted to the adder 1250-3 and 1250-4 instead of data levels dlev_(3L) and dlev_(0H), respectively. However, the sampler 1200 c is the same as the sampler 1200 a in that the outputs of the adders 1250-1, 1250-3 and 1250-4 are sampled at the rising edge of the corresponding clock, and the sampled data are outputted.

FIG. 9D is a block diagram illustrating a sampler which is a combination of the samplers shown in FIG. 9C and FIG. 5.

Referring to FIG. 9D, the sampler 1200 d of the PAM4 receiver according to the present invention is the same as the sampler 1200 b shown in FIG. 9B except the difference between the sampler 1200 c shown in FIG. 9C and the sampler 1200 a shown in FIG. 9A. Therefore, a detailed description thereof is omitted.

Referring back to FIG. 7, the DEMUX 1300 parallelizes the signal SAMPLE_out from the sampler 1200 and outputs the signal DATA_out.

Specifically, the DEMUX 1300 parallelizes, according to a predetermined clock, the signals DET[0], DOT[0], XET[0], XOT[0], DET[1], DOT[1], XET[1], XOT[1], DET[2], DOT[2], XET[2] and XOT[2] contained in the signal SAMPLE_out, and outputs the parallelized signals DET[2:0], DOT[2:0], XET[2:0] and XOT[2:0] as the signal DATA_out. More specifically, since the signals DET[0], DOT[0], XET[0], XOT[0], DET[1], DOT[1], XET[1], XOT[1], DET[2], DOT[2], XET[2] and XOT[2] contained in the signal SAMPLE_out are not simultaneously outputted, the signals DET[0], DOT[0], XET[0], XOT[0], DET[1], DOT[1], XET[1], XOT[1], DET[2], DOT[2], XET[2] and XOT[2] contained in the signal SAMPLE_out are parallelized (synchronized) according to a predetermined clock and outputted as the signal DATA_out. Similarly, the DEMUX 1300 may parallelize other signals outputted from the sampler 1200.

In addition, the DEMUX 1300 provides the signal DATA_out to the CDR 1400 and the controller 1500.

The CDR (Clock-and-Data Recovery) 1400 provides the sampling clock signals DCK, XCK, DCKB and XCKB to the sampler 1200 and the controller 1500.

Specifically, the CDR 1400 adjusts the timings or the phases of the sampling clock signals DCK, XCK, DCKB and XCKB based on the signal DET[2:0], DOT[2:0], XET[2:0], XOT[2:0]. Here, the sampling clock signal DCK, XCK, DCKB and XCKB are the same as those shown in FIG. 6.

More specifically, the CDR 1400 adjusts the phases of the sampling clock signal DCK, XCK, DCKB and XCKB according to the time point at which the signal CTLE_out passes the threshold voltage V_(TH12), that is, the time point at which a transition section of the signal CTLE_out and the threshold voltage V_(TH12) meet. For example, since the transition section of signal CTLE_out is sampled according to the clock signals XCK and XCKB, CDR 1400 determines the time point at which the signal CTLE_out passes the threshold voltage V_(TH12) at the rising edges of the clock signals XCK and XCKB, and adjusts the phases of the sampling clock signals DCK and DCKB such that the signal CTLE_out is sampled at the center of the symbol according to the clock signals DCK and DCKB.

The controller 1500 feeds a threshold voltage V_(TH01), V_(TH12), V_(TH23) and the data levels dlev_(3H), dlev_(3L), dlev₁ and dlev₂ to the sampler 1200, and generates signals EQ_AC[N_(AC)-1:0] and EQ_DC[N_(DC)-1:0] for selectively turning on or off a plurality of capacitors C_(unit) and a plurality of resistors R_(unit) included in the CTLE 1100, respectively in order to control high frequency amplification characteristics and low frequency amplification characteristics of the CTLE 1100.

Hereinafter, a method of training a PAM4 receiver according to the present invention will be described in detail.

The PAM4 receiver according to the present invention receives actual data after being tuned or trained by a training pattern. Specifically, the PAM4 receiver is used for actual communication after various parameters such as the threshold voltages V_(TH01), V_(TH12) and V_(TH23) are tuned using the training pattern.

The training pattern was created considering DC balance, timing of transitions, and facilitation of data level measurement. For DC balance, it is desirable to create the training pattern including combinations of “00” and “11” wherein the number of “00” and “11” are the same, and the number of “01” and “10” are the same. For the timing of the transition, it is desirable to select data in the training pattern such that the signal CTLE_out passes the threshold voltage V_(TH12) only when the transitions “00”→“11”, “11”→“00”, “01”→“10” and “10”→“01” occur. For facilitation of data level measurement, it is desirable to select data in the training pattern such that the number of each of “00”, “01”, “10” and “11” is equal to or more than two.

FIG. 10A and FIG. 10B are waveform diagrams of for describing the operation of the PAM4 receivers according to first and second embodiments of the present invention, respectively, wherein training patterns are shown.

The training pattern illustrated in FIG. 10A includes a first training data pattern and a second training data pattern. The training pattern includes four counts of data “00” and four counts of data “11”, and two counts of data “01” and two counts of data “10” in overall. Specifically, the first training data pattern includes one data “00” and consecutive first data “11” through fourth data “11” in order, and the second training data pattern includes combinations of “00” and “11” having two counts of data “00”, one count of data “01”, two counts of data “10”, one count of data “01” and two counts of data “00”. However, as described above, different combinations of “00”, “01”, “10” and “11” are possible by considering DC balance, timing of transitions, and ease of data level measurement. For example, the first training data pattern may include consecutive first data “11” through m^(th) data “11” in order where m is a natural number equal to or greater than 2.

The training pattern illustrated in FIG. 10B includes a first training data pattern and a second training data pattern. The training pattern includes four counts of data “00” and four counts of data “11”, and two counts of data “01” and two counts of data “10” in overall. Specifically, the first training data pattern includes one data “11” and consecutive first data “00” to fourth data “00” in order, and the second training data pattern includes combinations of “00” and “11” having two counts of data “11”, one count of data “10”, two counts of data “01”, one count of data “10” and two counts of data “11”. However, as described above, different combinations of “00”, “01”, “10” and “11” are possible by considering DC balance, timing of transitions, and ease of data level measurement. For example, the first training data pattern may include consecutive first data “00” through m^(th) data “00” in order where m is a natural number equal to or greater than 2.

Hereinafter, the method of training the PAM4 receiver according to the first embodiment and the second embodiment of the present invention will be described in detail with reference to FIGS. 10A, 10B, 11A and 11B.

FIG. 11A is a flow diagrams illustrating a method of training the PAM4 receivers according to the first embodiment of the present invention. It is preferable to use the sampler shown in FIG. 9A when training the PAM4 receiver according to the present invention using the training pattern exemplified in FIG. 10A. However, the present invention is not limited thereto.

First, for convenience of describing the present invention, equations

$V_{TH01} = \frac{{dlev_{0}} + {dlev}_{1}}{2}$ ${V_{TH12} = \frac{{dlev_{1}} + {dlev_{2}}}{2}}\;,\mspace{11mu}{{{and}\mspace{14mu} V_{TH23}} = \frac{{dlev_{2}} + {dlev}_{3}}{2}}$

are assumed. That is, the threshold voltages V_(TH01), V_(TH12) and V_(TH23) are calculated by the controller 1500 according to the equations and provided to the sampler 1200. In addition, predetermined initial values of the data levels dlev_(3H) and dlev_(3L) are stored in the controller 1500 in advance, and equation

${dlev_{3}} = \frac{{dlev_{3H}} + {dlev_{3L}}}{2}$

is assumed.

Referring to FIG. 11A, the CTLE 1100 of the PAM4 receiver according to the present invention receives a signal containing the training pattern shown in FIG. 10A (S100). Specifically, the CTLE 1100 shown in FIG. 7 receives the training pattern including the first training data pattern and the second training data pattern.

Thereafter, the CTLE 1100 equalizes the signal received in the step S100 based on the initial equalization parameter, and outputs the signal CTLE_out shown in FIG. 10A (S110). Here, the equalization parameter includes a high frequency amplification gain and a low frequency amplification gain of a linear equalizer.

Specifically, CTLE 1100 equalizes the received signal containing the training pattern according to the initial equalization parameter, and outputs the signal CTLE_out containing equalized first training data pattern and equalized second training data pattern.

Thereafter, the sampler 1200 a samples the signal CTLE_out at the rising edge of the clock signals DCK and DCKB to generate a signal SAMPLE_out (S120).

Specifically, The sampler 1200 a shown in FIG. 9A samples the difference dlev_(3HD) which is a difference between: the voltage level of the signal CTLE_out immediately after the transition from the data “00” to the first data “11” of the first training data pattern (i.e. a first voltage level of the signal CTLE_out (denoted by in ♦ FIG. 10A) corresponding to the first data “11” of the equalized first training data pattern when a transition from the data “00” to the first data “11” occurs); and a predetermined upper limit dlev_(3H). The sampled difference dlev_(3HD) is then outputted as the signal SAMPLE_out by the sampler 1200 a.

Here, the difference dlev_(3HD is) sampled by the flip-flops 1240-1 and 1240-2 shown in FIG. 9A at the rising edges of the clock signals DCK and DCKB, respectively, and outputted as signals AEd_(3H) and AOd_(3H), respectively. Each of the signals AEd_(3H) and AOd_(3H) may have value of “1” or “0” (representing whether the difference dlev_(3HD) is a positive number or a negative number) depending on the first voltage level (magnitude) of the signal CTLE_out.

In addition, the sampler 1200 a shown in FIG. 9A samples the difference dlev_(3LD) which is a difference between: a second voltage level of the signal CTLE_out (denoted by in FIG. 10A) corresponding to one of the data after the first data “11” of the first training data pattern (i.e. any one of the second data “11” through the m^(th) data “11” of the equalized first training data pattern, where m is a natural number equal to or greater than 2, and an example wherein m=4 is shown in FIG. 10A); and a predetermined lower limit dlev_(3L). The sampled difference dlev_(3LD) is then outputted as the signal SAMPLE_out by the sampler 1200 a.

Here, the difference dlev_(3LD) is sampled by the flip-flops 1230-1 and 1230-2 shown in FIG. 9A at the rising edges of the clock signals DCK and DCKB, respectively, and outputted as signals AEd_(3L) and AOd_(3L), respectively. Each of the signals AEd_(3L) and AOd_(3L) may have value of “1” or “0” (representing whether the difference dlev_(3LD) is a positive number or a negative number) depending on the voltage level (magnitude) of the signal CTLE_out.

Thereafter, the signal SAMPLE_out outputted by the sampler 1200 a is parallelized and the parallelized signal SAMPLE_out is outputted as the signal DATA_out (S130). Specifically, the DEMUX 1300 generates the signal DATA_out by parallelizing the signal SAMPLE_out. Here, since the signal DATA_out is obtained by parallelizing signal SAMPLE_out, the signal DATA_out contains the signals included in the signal SAMPLE_out of the sampler 1200 such as the differences dlev_(3HD) and dlev_(3LD).

Thereafter, the signals EQ_AC[N_(AC)-1:0] and EQ_DC[N_(DC)-1:0] for adjusting the high and the low frequency amplification gains of the CTLE 1100, respectively, are generated from the signal DATA_out (S140).

Specifically, the signals EQ_AC[N_(AC)-1:0] and EQ_DC[N_(DC)-1:0] are generated based on the first training data pattern which is used for adjusting the high and the low frequency amplification gains of the CTLE 1100.

Hereinafter, a method of generating the signal EQ_AC[N_(AC)-1:0] will be described in detail, and a method of generating the signal EQ_DC[N_(DC)-1:0] will be described in detail thereafter.

The signal EQ_AC[N_(AC)-1:0] is generated based on the difference dlev_(3HD) contained in the signal DATA_out.

Specifically, as described above, the difference dlev_(3HD) is the difference between: the first voltage level of the signal CTLE_out (denoted by in FIG. 10A); and the upper limit dlev_(3H). The reason for generating the signal EQ_AC[N_(AC)-1:0] and using the same to adjust the high frequency amplification gain of CTLE 1100 is to make the first voltage level of the signal CTLE_out equal to the upper limit dlev_(3H).

In the case of the example shown in FIG. 10A, the difference dlev_(3HD) has a negative value since the first voltage level of the signal CTLE_out is lower than the upper limit dlev_(3H).

As a result, the first voltage level of the signal CTLE_out should be increased in the example shown in FIG. 10A since the goal is to make the first voltage level of the signal CTLE_out equal to the upper limit dlev_(3H).

However, when the transition from the data “00” to the first data “11” of the first training data pattern occurs, the first voltage level of the signal CTLE_out corresponding to the first data “11” varies depending on the high frequency amplification gain of CTLE 1100. Therefore, in order to increase the first voltage level of the signal CTLE_out, the controller 1500 generates the signal EQ_AC[N_(AC)-1:0] that increases the high frequency amplification gain of the CTLE 1100 and provides the same to the CTLE 1100. For example, the controller 1500 generates the signal EQ_AC[N_(AC)-1:0] with increased number of value “1” contained therein and provides the same to the CTLE 1100 such that the number of capacitors C_(unit) turned on by the signal EQ_AC[N_(AC)-1:0] increases.

On the other hand, when the first voltage level of the signal CTLE_out is higher than the upper limit dlev_(3H), the difference dlev_(3HD) has a positive value.

Similarly, the first voltage level of the signal CTLE_out should be decreased since the goal is to make the first voltage level of the signal CTLE_out equal to the upper limit dlev_(3H),

However, when the transition from the data “00” to the first data “11” of the first training data pattern occurs, the first voltage level of the signal CTLE_out corresponding to the first data “11” varies depending on the high frequency amplification gain of CTLE 1100. Therefore, in order to decrease the first voltage level of the signal CTLE_out, the controller 1500 generates the signal EQ_AC[N_(AC)-1:0] that decreases the high frequency amplification gain of the CTLE 1100 and provides the same to the CTLE 1100. For example, the controller 1500 the signal EQ_AC[N_(AC)-1:0] with increased number of value “0” contained therein and provides the same to the CTLE 1100 such that the number of capacitors C_(unit) turned on by the signal EQ_AC[N_(AC)-1:0] decreases.

The signal EQ_DC[N_(DC)-1:0] is generated based on the difference dlev_(3LD) contained in the signal DATA_out.

Specifically, as described above, the difference dlev_(3LD) is the difference between: the second voltage level of the signal CTLE_out (denoted by in FIG. 10A); and the lower limit dlev_(3L). The reason for generating the signal EQ_DC[N_(DC)-1:0] and using the same to adjust the low frequency amplification gain of CTLE 1100 is to make the second voltage level of the signal CTLE_out equal to the lower limit dlev_(3L).

In the case of the example shown in FIG. 10A, the difference dlev_(3LD) has a positive value since the second voltage level of the signal CTLE_out is higher than the lower limit dlev_(3L).

As a result, the second voltage level of the signal CTLE_out should be decreased in the example shown in FIG. 10A since the goal is to make the second voltage level of the signal CTLE_out equal to the lower limit dlev_(3L).

However, the second voltage level of the signal CTLE_out corresponding to any one of the second data “11” through the m^(th) data “11” of the equalized first training data pattern varies depending on the low frequency amplification gain of CTLE 1100. Therefore, in order to decrease the second voltage level of the signal CTLE_out, the controller 1500 generates the signal EQ_DC[N_(DC)-1:0] that decreases the low frequency amplification gain of the CTLE 1100 and provides the same to the CTLE 1100. For example, the controller 1500 generates the signal EQ_DC[N_(DC)-1:0] with increased number of value “0” contained therein and provides the same to the CTLE 1100 such that the number of resistors R_(unit) turned on by the signal EQ_DC[N_(DC)-1:0] decreases.

On the other hand, when the second voltage level of the signal CTLE_out is lower than the lower limit dlev_(3L), the difference dlev_(3LD) has a negative value.

Similarly, the second voltage level of the signal CTLE_out should be increased since the goal is to make the second voltage level of the signal CTLE_out equal to the lower limit dlev_(3L),

However, the second voltage level of the signal CTLE_out corresponding to any one of the second data “11” through the m^(th) data “11” of the equalized first training data pattern varies depending on the low frequency amplification gain of CTLE 1100. Therefore, in order to increase the second voltage level of the signal CTLE_out, the controller 1500 generates the signal EQ_DC[N_(DC)-1:0] that increases the low frequency amplification gain of the CTLE 1100 and provides the same to the CTLE 1100. For example, the controller 1500 generates the signal EQ_DC[N_(DC)-1:0] with increased number of value “1” contained therein and provides the same to the CTLE 1100 such that the number of resistors R_(unit) turned on by the signal EQ_DC[N_(DC)-1:0] increases.

Thereafter, the threshold voltages V_(TH01), V_(TH12) and V_(TH23) of the sampler 1200 a (or the sampler 1200 b) are generated from the data level dlev₁ or dlev₂ (S150).

Specifically, the data level dlev₁ or dlev₂ is generated from the difference dlev_(1D) or dlev_(2D), respectively, and the threshold voltages V_(TH01), V_(TH12) and V_(TH23) of the sampler 1200 a (or the sampler 1200 b) are generated from the upper limit dlev_(3H), the lower limit dlev_(3L) and the data levels dlev₀, dlev₁, dlev₂ and dlev₃.

The step S150 includes a step S150 a and a step S150 b shown in FIG. 12A. Hereinafter, the step S150 will be described in detail with reference to FIG. 12A.

Referring to FIG. 12A, the data levels dlev₁ and dlev₂ are determined according to the signs of the differences dlev_(1D) and dlev_(2D), respectively (S150 a).

Specifically, the data levels dlev₁ and dlev₂ are determined using the second training data pattern.

As shown in FIG. 9A, the sampler 1200 a samples the difference dlev_(1D) which is a difference between: a third voltage level (denoted by ● in FIG. 10A) of the signal CTLE_out corresponding to the data “01” of the second training data pattern at the rising edge of the clock signals DCK and DCKB; and the data level dlev₁. Here, the data level dlev₁ has an initial value, and the controller 1500 then adjusts the data level dlev₁ according to the sign of the difference dlev_(1D). That is, depending on which one of the third voltage level of the signal CTLE_out and the data level dlev₁ is higher, the data level dlev₁ is increased or decreased by a predetermined value.

While the sampler 1200 a samples the difference dlev_(1D) in FIG. 9A, the difference dlev_(2D), which is a difference between: a fourth voltage level (denoted by ▴ in FIG. 10A) of the signal CTLE_out corresponding to the data “10” of the second training data pattern at the rising edge of the clock signals DCK and DCKB; and the data level dlev₂, may also be sampled. In particular, when the data levels dlev₁ and dlev₂ have the same magnitude and opposite signs (i.e., dlev₂=−dlev₁), it is sufficient when only one of the data levels dlev₁ and dlev₂ is determined since the other can be automatically determined. However, when the data levels dlev₁ and dlev₂ have different magnitudes or have the same sign, both of the differences dlev_(1D) and dlev_(2D) may be sampled to adjust both of the data levels dlev₁ and dlev₂.

Thereafter, the threshold voltages V_(TH01), V_(TH12) and V_(TH23) of the sampler 1200 a (or the sampler 1200 b) are calculated from the upper limit dlev_(3H), the lower limit dlev_(3L) and the data levels dlev₀, dlev₁, dlev₂ and dlev₃ according to the equation 1 below (S150 b).

$\begin{matrix} {{{{dle}v_{3}} = \frac{{dlev_{3H}} + {dlev_{3L}}}{2}},{V_{TH01} = \frac{{dlev_{0}} + {dlev}_{1}}{2}},} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack \\ {{V_{TH12} = \frac{{dlev_{1}} + {dlev_{2}}}{2}}\;,{V_{TH23} = \frac{{dlev_{2}} + {dlev}_{3}}{2}}} & \; \end{matrix}$

Thereafter, as shown in FIG. 11A, the equalization parameter is adaptively adjusted according to the signals EQ_AC[N_(AC)-1:0] and EQ_DC[N_(DC)-1:0] generated in the step S140 (S160).

The step S160 will be described in detail with reference to FIG. 13A,

Referring to FIG. 13A, the plurality of capacitors C_(unit) included in the CTLE 1100 are selectively turned on using the signal EQ_AC[N_(AC)-1:0] generated in the step S140 to adjust the high frequency amplification gain of the CTLE 1100 (S160 a).

Thereafter, the plurality of resistors R_(unit) included in the CTLE 1100 are selectively turn on using the signal EQ_DC[N_(DC)-1:0] generated in step S140 to adjust the low frequency amplification gain of the CTLE 1100 (S160 b).

Thereafter, it is determined whether the high frequency amplification gain of the CTLE 1100 is at its maximum (S160 c). The reason for determining whether the high frequency amplification gain is at its maximum is to determine whether the upper limit dlev_(3H) is excessively high. For example, when the first voltage level of the signal CTLE_out is lower than the upper limit dlev_(3H) even with the high frequency amplification gain at its maximum by turning on entirety of N_(AC) capacitors C_(unit), the upper limit dlev_(3H) must be lowered as the high frequency amplification gain cannot be increased any further. Therefore, it is necessary to determine whether the high frequency amplification gain is at its maximum.

When the high frequency amplification gain is not at its maximum (“N” in step S160 c), the step S160 ends since the high frequency amplification gain can be further increased if necessary.

On the other hand, when the high frequency amplification gain is at its maximum (“Y” in step S160 c), it is determined that which one of the first voltage level of the signal CTLE_out and the upper limit dlev_(3H) is higher (S160 d).

When the first voltage level of the signal CTLE_out is lower than the upper limit dlev_(3H) even with the high frequency amplification gain at its maximum (“Y” in step S160 d), the upper limit dlev_(3H) and the lower limit dlev_(3L) are lowered as the high frequency amplification gain cannot be increased any further (S160 e).

When the first voltage level of the signal CTLE_out is higher than or equal to the upper limit dlev_(3H) (“N” in step S160 d), the step S160 ends.

The steps S160 c through S160 e for lowering the upper limit dlev_(3H) and the lower limit dlev_(3L) may be performed when the steps S100 through S170 shown in FIG. 11A are repeatedly performed.

For example, when the first voltage level of the signal CTLE_out obtained from the (k+1)^(th) first training data pattern (where k is a natural number equal to or greater than 2) is not as high as the upper limit dlev_(3H) although the high frequency amplification gain was adjusted to its maximum due to the insufficient first voltage level of the signal CTLE_out obtained from the k^(th) first training data pattern, the controller 1500 may lower both of the upper limit dlev_(3H) and the lower limit dlev_(3L) instead of adjusting the high frequency amplification gain. That is, after lowering the upper limit dlev_(3H) and the lower limit dlev_(3L) until the first voltage level of the signal CTLE_out is between the upper limit dlev_(3H) and lower limit dlev_(3L), the high frequency amplification gain may then be tuned.

Thereafter, as shown in FIG. 11A, the sampling parameter of the sampler is adaptively adjusted according to the data levels dlev₁ and dlev₂, the upper limit dlev_(3H), the lower limit dlev_(3L) and the threshold voltages V_(TH01), V_(TH12) and V_(TH23) generated in step S150 (S170).

Thereafter, it is determined whether the value of the difference dlev_(3HD), the difference dlev_(3LD), the difference dlev_(1D) or the difference dlev_(2D) is zero (S180).

Specifically, when the value of the difference dlev_(3HD), the difference dlev_(3LD), the difference dlev_(1D) or the difference dlev_(2D) is zero (“Y” in step S180), the method of training PAM4 receiver according to the first embodiment is ended. When the value of the difference dlev_(3HD), dlev_(3LD), dlev_(1D) or dlev_(2D) is not zero (“N” in step S180), the steps S100 through S170 are repeated until the difference dlev_(3HD), dlev_(3LD), dlev_(1D) or dlev_(2D) becomes zero.

Here, it is not necessary that the values of the differences dlev_(3HD), dlev_(3LD), dlev_(1D) and dlev_(2D) be all zero. For example, the steps S100 through S170 may be repeated until the values of the differences dlev_(3HD) and dlev_(3LD) becomes all zero, until the value of the difference dlev_(3HD) becomes zero, or until the values of the differences dlev_(3HD), dlev_(3LD), dlev_(1D), and dlev_(2D) become all zero. In other words, it is possible to select conditions of the repetition as necessary.

The repetition of the steps S100 through S170 means performing the steps S100 through S170 each time the same training pattern (e.g. the training pattern shown in FIG. 10A) is received.

The reason for repeating the steps S100 through S170 is to achieve the goal which is to make the voltage level of the first signal CTLE_out equal to the upper limit dlev_(3H), and the second voltage level of the signal CTLE_out equal to the lower limit dlev_(3L).

In order to achieve this, the high frequency amplification gain and the low frequency amplification gain must be adjusted such that the values of the differences dlev_(3HD), dlev_(3LD), dlev_(1D) and dlev_(2D) become zero or converge to zero. Specifically, since the voltage levels of the signal CTLE_out approaches the upper limit dlev_(3H) and lower limit dlev_(3L) each time the steps S100 through S170 is performed by adjusting the high frequency amplification gain and the low frequency amplification gain, the values of the differences dlev_(3HD), dlev_(3LD), dlev_(1D) and dlev_(2D) become zero or converge to zero as the steps S100 through S170 are repeated.

For example, after the tuning of the high frequency amplification gain and the low frequency amplification gain using a j^(th) training pattern (where j is a natural number) is complete, a (j+1)^(th) training pattern, which is the same as the j^(th) training pattern, is received and used to tune the high frequency amplification gain and the low frequency amplification gain by repeating the same process as described above.

Specifically, the sampler 1200 a samples the difference dlev_(3HD) between: the first voltage level of the signal CTLE_out corresponding to the data “11” of the (j+1)^(th) first training data pattern when the transition from the data “00” to the first data “11” occurs; and the upper limit dlev_(3H). Since the signal CTLE_out is the output of CTLE 1100 already trained using the j^(th) first training data pattern, the difference dlev_(3HD) between: the first voltage level of the signal CTLE_out obtained from the (j+1)^(th) first training data pattern; and the upper limit dlev_(3H) is smaller than the difference dlev_(3HD) between: the first voltage level of the signal CTLE_out obtained from the j^(th) first training data pattern; and the upper limit dlev_(3H). Accordingly, the high frequency amplification gain of the CTLE 1100 may be fine-tuned by a more precise signal EQ_AC[N_(AC)-1:0] generated by the controller 1500.

Similarly, the difference dlev_(3LD) obtained from the (j+1)^(th) first training data pattern is smaller than the difference dlev_(3LD) obtained from the j^(th) first training data pattern. Accordingly, the low frequency amplification gain of the CTLE 1100 may be fine-tuned by a more precise signal EQ_DC[N_(DC)-1:0] generated by the controller 1500.

In addition, since the differences dlev_(1D) and dlev_(2D) obtained from the (j+1)^(th) second training data pattern are smaller than the differences dlev_(1D) and dlev_(2D) obtained from the j^(th) second training data pattern, more precise data levels dlev₁ and dlev₂ may be obtained.

As described above, when the PAM4 receiver is trained by repeatedly receiving the same training pattern until the differences dlev_(3HD), dlev_(3LD), dlev_(1D) and dlev_(2D) become zero or converge to zero, the PAM4 signal received during the actual use of the PAM4 receiver may be precisely determined despite the attenuation of the transmission line.

FIG. 11B is a flow diagrams illustrating a method of training the PAM4 receivers according to the first embodiment of the present invention. It is preferable to use the sampler shown in FIG. 9C when training the PAM4 receiver according to the present invention using the training pattern exemplified in FIG. 10B. However, the present invention is not limited thereto.

First, for convenience of describing the present invention, equations

${V_{TH01} = \frac{{dlev_{0}} + {dlev}_{1}}{2}},{V_{TH12} = \frac{{dlev_{1}} + {dlev_{2}}}{2}}\;,{and}$ $V_{TH23} = \frac{{dlev_{2}} + {dlev}_{3}}{2}$

are assumed. That is, the threshold voltages V_(TH01), V_(TH12) and V_(TH23) are calculated by the controller 1500 according to the equations and provided to the sampler 1200. In addition, predetermined initial values of the data levels dlev_(0L) and dlev_(0L) are stored in the controller 1500 in advance, and equation

${dlev}_{0} = \frac{{dlev_{0H}} + {dlev_{0L}}}{2}$

is assumed.

Referring to FIG. 11B, the CTLE 1100 of the PAM4 receiver according to the present invention receives a signal containing the training pattern shown in FIG. 10B (S200). Specifically, the CTLE 1100 shown in FIG. 7 receives the training pattern including the first training data pattern and the second training data pattern.

Thereafter, the CTLE 1100 equalizes the signal received in the step S200 based on the initial equalization parameter, and outputs the signal CTLE_out shown in FIG. 10B (S210). Here, the equalization parameter includes a high frequency amplification gain and a low frequency amplification gain of a linear equalizer.

Specifically, CTLE 1100 equalizes the received signal containing the training pattern according to the initial equalization parameter, and outputs the signal CTLE_out containing equalized first training data pattern and equalized second training data pattern

Thereafter, the sampler 1200 c samples the signal CTLE_out at the rising edge of the clock signals DCK and DCKB to generate a signal SAMPLE_out (S220).

Specifically, The sampler 1200 c shown in FIG. 9C samples the difference dlev_(0HD) which is a difference between: the voltage level of the signal CTLE_out immediately after the transition from the data “11” to the first data “00” of the first training data pattern (i.e. a first voltage level of the signal CTLE_out (denoted by in 567 FIG. 10B) corresponding to the first data “00” of the equalized first training data pattern when a transition from the data “11” to the first data “00” occurs); and a predetermined lower limit dlev_(0L). The sampled difference dlev_(0LD) is then outputted as the signal SAMPLE_out by the sampler 1200 c.

Here, the difference dlev_(0HD) is sampled by the flip-flops 1240-1 and 1240-2 shown in FIG. 9C at the rising edges of the clock signals DCK and DCKB, respectively, and outputted as signals AEd_(0L) and AOd_(0L), respectively. Each of the signals AEd_(0L) and AOd_(0L) may have value of “1” or “0” (representing whether the difference dlev_(0LD) is a positive number or a negative number) depending on the first voltage level (magnitude) of the signal CTLE_out.

In addition, the sampler 1200 c shown in FIG. 9C samples the difference dlev_(0LD) which is a difference between: a second voltage level of the signal CTLE_out (denoted by in ▪ FIG. 10B) corresponding to one of the data after the first data “00” of the first training data pattern (i.e. any one of the second data “00” through the m^(th) data “00” of the equalized first training data pattern, where m is a natural number equal to or greater than 2, and an example wherein m=4 is shown in FIG. 10B); and a predetermined upper limit dlev_(0H). The sampled difference dlev_(0HD) is then outputted as the signal SAMPLE_out by the sampler 1200 c.

Here, the difference dlev_(0HD) is sampled by the flip-flops 1230-1 and 1230-2 shown in FIG. 9C at the rising edges of the clock signals DCK and DCKB, respectively, and outputted as signals AEd_(0H) and AOd_(0H), respectively. Each of the signals AEd_(0H) and AOd_(0H) may have value of “1” or “0” (representing whether the difference dlev_(0HD) is a positive number or a negative number) depending on the voltage level (magnitude) of the signal CTLE_out.

Thereafter, the signal SAMPLE_out outputted by the sampler 1200 c is parallelized and the parallelized signal SAMPLE_out is outputted as the signal DATA_out (S230). Specifically, the DEMUX 1300 generates the signal DATA_out by parallelizing the signal SAMPLE_out. Here, since the signal DATA_out is obtained by parallelizing signal SAMPLE_out, the signal DATA_out contains the signals included in the signal SAMPLE_out of the sampler 1200 such as the differences dlev_(0LD) and dlev_(0HD).

Thereafter, the signals EQ_AC[N_(AC)-1:0] and EQ_DC[N_(DC)-1:0] for adjusting the high and the low frequency amplification gains of the CTLE 1100, respectively, are generated from the signal DATA_out (S240).

Specifically, the signals EQ_AC[N_(AC)-1:0] and EQ_DC[N_(DC)-1:0] are generated based on the first training data pattern which is used for adjusting the high and the low frequency amplification gains of the CTLE 1100.

Hereinafter, a method of generating the signal EQ_AC[N_(AC)-1:0] will be described in detail, and a method of generating the signal EQ_DC[N_(DC)-1:0] will be described in detail thereafter.

The signal EQ_AC[N_(AC)-1:0] is generated based on the difference dlev_(0LD) contained in the signal DATA_out.

Specifically, as described above, the difference dlev_(0LD) is the difference between: the first voltage level of the signal CTLE_out (denoted by in ♦ FIG. 10B); and the lower limit dlev_(0L). The reason for generating the signal EQ_AC[N_(AC)-1:0] and using the same to adjust the high frequency amplification gain of CTLE 1100 is to make the first voltage level of the signal CTLE_out equal to the lower limit dlev_(0L).

In the case of the example shown in FIG. 10B, the difference dlev_(0LD) has a positive value since the first voltage level of the signal CTLE_out is higher than the lower limit dlev_(0L).

As a result, the first voltage level of the signal CTLE_out should be decreased in the example shown in FIG. 10B since the goal is to make the first voltage level of the signal CTLE_out equal to the lower limit dlev_(0L).

However, when the transition from the data “11” to the first data “00” of the first training data pattern occurs, the first voltage level of the signal CTLE_out corresponding to the first data “00” varies depending on the high frequency amplification gain of CTLE 1100. Therefore, in order to decrease the first voltage level of the signal CTLE_out, the controller 1500 generates the signal EQ_AC[N_(AC)-1:0] that increases the high frequency amplification gain of the CTLE 1100 and provides the same to the CTLE 1100. For example, the controller 1500 generates the signal EQ_AC[N_(AC)-1:0] with increased number of value “1” contained therein and provides the same to the CTLE 1100 such that the number of capacitors C_(unit) turned on by the signal EQ_AC[N_(AC)-1:0] increases.

On the other hand, when the first voltage level of the signal CTLE_out is lower than the lower limit dlev_(0L), the difference dlev_(0LD) has a negative value.

Similarly, the first voltage level of the signal CTLE_out should be increased since the goal is to make the first voltage level of the signal CTLE_out equal to the lower limit dlev_(0L),

However, when the transition from the data “11” to the first data “00” of the first training data pattern occurs, the first voltage level of the signal CTLE_out corresponding to the first data “00” varies depending on the high frequency amplification gain of CTLE 1100. Therefore, in order to increase the first voltage level of the signal CTLE_out, the controller 1500 generates the signal EQ_AC[N_(AC)-1:0] that decreases the high frequency amplification gain of the CTLE 1100 and provides the same to the CTLE 1100. For example, the controller 1500 the signal EQ_AC[N_(AC)-1:0] with increased number of value “0” contained therein and provides the same to the CTLE 1100 such that the number of capacitors C_(unit) turned on by the signal EQ_AC[N_(AC)-1:0] decreases.

The signal EQ_DC[N_(DC)-1:0] is generated based on the difference dlev_(0HD) contained in the signal DATA_out.

Specifically, as described above, the difference dlev_(0HD) is the difference between: the second voltage level of the signal CTLE_out (denoted by in ▪ FIG. 10B); and the upper limit dlev_(0H). The reason for generating the signal EQ_DC[N_(DC)-1:0] and using the same to adjust the low frequency amplification gain of CTLE 1100 is to make the second voltage level of the signal CTLE_out equal to the upper limit dlev_(0H).

In the case of the example shown in FIG. 10B, the difference dlev_(0HD) has a positive value since the second voltage level of the signal CTLE_out is higher than the upper limit dlev_(0H).

As a result, the second voltage level of the signal CTLE_out should be decreased in the example shown in FIG. 10B since the goal is to make the second voltage level of the signal CTLE_out equal to the upper limit dlev_(0H).

However, the second voltage level of the signal CTLE_out corresponding to any one of the second data “00” through the m^(th) data “00” of the equalized first training data pattern varies depending on the low frequency amplification gain of CTLE 1100. Therefore, in order to decrease the second voltage level of the signal CTLE_out, the controller 1500 generates the signal EQ_DC[N_(DC)-1:0] that increases the low frequency amplification gain of the CTLE 1100 and provides the same to the CTLE 1100. For example, the controller 1500 generates the signal EQ_DC[N_(DC)-1:0] with increased number of value “1” contained therein and provides the same to the CTLE 1100 such that the number of resistors R_(unit) turned on by the signal EQ_DC[N_(DC)-1:0] increases.

On the other hand, when the second voltage level of the signal CTLE_out is lower than the upper limit dlev_(0H), the difference dlev_(0HD) has a negative value.

Similarly, the second voltage level of the signal CTLE_out should be increased since the goal is to make the second voltage level of the signal CTLE_out equal to the upper limit dlev_(0H),

However, the second voltage level of the signal CTLE_out corresponding to any one of the second data “00” through the m^(th) data “00” of the equalized first training data pattern varies depending on the low frequency amplification gain of CTLE 1100. Therefore, in order to increase the second voltage level of the signal CTLE_out, the controller 1500 generates the signal EQ_DC[N_(DC)-1:0] that decreases the low frequency amplification gain of the CTLE 1100 and provides the same to the CTLE 1100. For example, the controller 1500 generates the signal EQ_DC[N_(DC)-1:0] with increased number of value “0” contained therein and provides the same to the CTLE 1100 such that the number of resistors R_(unit) turned on by the signal EQ_DC[N_(DC)-1:0] decreases.

Thereafter, the threshold voltages V_(TH01), V_(TH12) and V_(TH23) of the sampler 1200 c (or the sampler 1200 d) are generated from the data level dlev₁ or dlev₂ (S250).

Specifically, the data level dlev₁ or dlev₂ is generated from the difference dlev_(1D) or dlev_(2D), respectively, and the threshold voltages V_(TH01), V_(TH12) and V_(TH23) of the sampler 1200 c (or the sampler 1200 d) are generated from the lower limit dlev_(0L), the upper limit dlev_(0H) and the data levels dlev₀, dlev₁, dlev₂ and dlev₃.

The step S250 includes a step S250 a and a step S250 b shown in FIG. 12B. Hereinafter, the step S250 will be described in detail with reference to FIG. 12B.

Referring to FIG. 12B, the data level dlev₁ and dlev₂ are determined according to the signs of the differences dlev_(1D) and dlev_(2D), respectively (S250 a).

Specifically, the data levels dlev₁ and dlev₂ are determined using the second training data pattern.

As shown in FIG. 9C, the sampler 1200 c samples the difference dlev_(2D) which is a difference between: a third voltage level (denoted by in ▴ FIG. 10B) of the signal CTLE_out corresponding to the data “10” of the second training data pattern at the rising edge of the clock signals DCK and DCKB; and the data level dlev₂. Here, the data level dlev₂ has an initial value, and the controller 1500 then adjusts the data level dlev₂ according to the sign of the difference dlev_(2D). That is, depending on which one of the third voltage level of the signal CTLE_out and the data level dlev₂ is higher, the data level dlev₂ is increased or decreased by a predetermined value.

While the sampler 1200 c samples the difference dlev_(2D) in FIG. 9C, the difference dlev_(1D), which is a difference between: a fourth voltage level (denoted by in ● FIG. 10B) of the signal CTLE_out corresponding to the data “01” of the second training data pattern at the rising edge of the clock signals DCK and DCKB; and the data level dlev₁, may be sampled. In particular, when the data levels dlev₁ and dlev₂ have the same magnitude and opposite signs (i.e., dlev₂=−dlev₁), it is sufficient when only one of the data levels dlev₁ and dlev₂ is determined since the other can be automatically determined. However, when the data levels dlev₁ and dlev₂ have different magnitudes or have the same sign, both of the differences dlev_(1D) and dlev_(2D) may be sampled to adjust both of the data levels dlev₁ and dlev₂.

Thereafter, the threshold voltages V_(TH01), V_(TH12) and V_(TH23) of the sampler 1200 c (or the sampler 1200 d) are calculated from the lower limit dlev_(0L), the upper limit dlev_(0H) and the data levels dlev₀, dlev₁, dlev₂ and dlev₃ according to the equation 2 below (S250 b).

$\begin{matrix} {{{dlev}_{0} = \frac{{dlev_{0H}} + {dlev_{0L}}}{2}},{V_{TH01} = \frac{{dlev_{0}} + {dlev}_{1}}{2}},{V_{TH12} = \frac{{dlev_{1}} + {dlev_{2}}}{2}},{V_{TH23} = \frac{{dlev_{2}} + {dlev}_{3}}{2}}} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack \end{matrix}$

Thereafter, as shown in FIG. 11B, the equalization parameter is adaptively adjusted according to the signals EQ_AC[N_(AC)-1:0] and EQ_DC[N_(DC)-1:0] generated in the step S240 (S260).

The step S260 will be described in detail with reference to FIG. 13B.

Referring to FIG. 13B, the plurality of capacitors C_(unit) included in the CTLE 1100 are selectively turned on using the signal EQ_AC[N_(AC)-1:0] generated in the step S240 to adjust the high frequency amplification gain of the CTLE 1100 (S260 a).

Thereafter, the plurality of resistors R_(unit) included in the CTLE 1100 are selectively turn on using the signal EQ_DC[N_(DC)-1:0] generated in step S240 to adjust the low frequency amplification gain of the CTLE 1100 (S260 b).

Thereafter, it is determined whether the high frequency amplification gain of the CTLE 1100 is at its maximum (S260 c). The reason for determining whether the high frequency amplification gain is at its maximum is to determine whether the lower limit dlev_(0L) is excessively low. For example, when the first voltage level of the signal CTLE_out is higher than the lower limit dlev_(0L) even with the high frequency amplification gain at its maximum by turning on entirety of N_(AC) capacitors C_(unit), the lower limit dlev_(0L) must be elevated as the high frequency amplification gain cannot be increased any further. Therefore, it is necessary to determine whether the high frequency amplification gain is at its maximum.

When the high frequency amplification gain is not at its maximum (“N” in step S260 c), the step S260 ends since the high frequency amplification gain can be further increased if necessary.

On the other hand, when the high frequency amplification gain is at its maximum (“Y” in step S260 c), it is determined that which one of the first voltage level of the signal CTLE_out and the lower limit dlev_(0L) is higher (S260 d).

When the first voltage level of the signal CTLE_out is higher than the lower limit dlev_(0L) even with the high frequency amplification gain at its maximum (“Y” in step S260 d), the lower limit dlev_(0L) and the upper limit dlev_(0H) are elevated as the high frequency amplification gain cannot be increased any further (S260 e).

When the first voltage level of the signal CTLE_out is lower than or equal to the lower limit dlev_(0L) (“N” in step S260 d), the step S260 ends.

The steps S260 c through S260 e for elevating the lower limit dlev_(0L) and the upper limit dlev_(0H) may be performed when the steps S200 through S270 shown in FIG. 11B are repeatedly performed.

For example, when the first voltage level of the signal CTLE_out obtained from the (k+1)^(th) first training data pattern (where k is a natural number equal to or greater than 2) is not as low as the lower limit dlev_(0L) although the high frequency amplification gain was adjusted to its maximum due to the insufficient first voltage level of the signal CTLE_out obtained from the k^(th) first training data pattern, the controller 1500 may elevate both of the lower limit dlev_(0L) and the upper limit dlev_(0H) instead of adjusting the high frequency amplification gain. That is, after elevating the lower limit dlev_(0L) and the upper limit dlev_(0H) until the first voltage level of the signal CTLE_out is between the lower limit dlev_(0L) and upper limit dlev_(0H), the high frequency amplification gain may then be tuned.

Thereafter, as shown in FIG. 11B, the sampling parameter of the sampler is adaptively adjusted according to the data levels dlev₁ and dlev₂, the lower limit dlev_(0L), the upper limit dlev_(0H) and the threshold voltages V_(TH01), V_(TH12) and V_(TH23) generated in step S250 (S270).

Thereafter, it is determined whether the value of the difference dlev_(0LD), the difference dlev_(0HD), the difference dlev_(1D) or the difference dlev_(2D) is zero (S280).

Specifically, when the value of the difference dlev_(0LD), the difference dlev_(0HD), the difference dlev_(1D) or the difference dlev_(2D) is zero (“Y” in step S280), the method of training PAM4 receiver according to the first embodiment is ended. When the value of the difference dlev_(0LD), dlev_(0HD), dlev_(1D) or dlev_(2D) is not zero (“N” in step S280), the steps S200 through S270 are repeated until the difference dlev_(0LD), dlev_(0HD), dlev^(1D) or dlev_(2D) becomes zero.

Here, it is not necessary that the values of the differences dlev_(0LD), dlev_(0HD), dlev_(1D) and dlev_(2D) be all zero. For example, the steps S200 through S270 may be repeated until the values of the differences dlev_(0LD) and dlev_(0HD) becomes all zero, until the value of the difference dlev_(0LD) becomes zero, or until the values of the differences dlev_(0LD), dlev_(0HD), dlev_(1D), and dlev_(2D) become all zero. In other words, it is possible to select conditions of the repetition as necessary.

The repetition of the steps S200 through S270 means performing the steps S200 through S270 each time the same training pattern (e.g. the training pattern shown in FIG. 10B) is received.

The reason for repeating the steps S200 through S270 is to achieve the goal which is to make the first voltage level of the signal CTLE_out equal to the lower limit dlev_(0L) and the second voltage level of the signal CTLE_out equal to the upper limit dlev_(0H).

In order to achieve this, the high frequency amplification gain and the low frequency amplification gain must be adjusted such that the values of the differences dlev_(0LD), dlev_(0HD), dlev_(1D) and dlev_(2D) become zero or converge to zero. Specifically, since the voltage levels of the signal CTLE_out approaches the lower limit dlev_(0L) and upper limit dlev_(0H) each time the steps S200 through S270 is performed by adjusting the high frequency amplification gain and the low frequency amplification gain, the values of the differences dlev_(0LD), dlev_(0HD), dlev_(1D) and dlev_(2D) become zero or converge to zero as the steps S200 through S270 are repeated.

For example, after the tuning of the high frequency amplification gain and the low frequency amplification gain using a j^(th) training pattern (where j is a natural number) is complete, a (j+1)^(th) training pattern, which is the same as the ij^(th) training pattern, is received and used to tune the high frequency amplification gain and the low frequency amplification gain by repeating the same process as described above.

Specifically, the sampler 1200 c samples the difference dlev_(0LD) between: the first voltage level of the signal CTLE_out corresponding to the data “00” of the (j+1)^(th) first training data pattern when the transition from the data “11” to the first data “00” occurs; and the lower limit dlev_(0L). Since the signal CTLE_out is the output of CTLE 1100 already trained using the j^(th) first training data pattern, the difference dlev_(0LD) between: the first voltage level of the signal CTLE_out obtained from the (j+1)^(th) first training data pattern; and the lower limit dlev_(0L) is smaller than the difference dlev_(0LD) between: the first voltage level of the signal CTLE_out obtained from the j^(th) first training data pattern; and the lower limit dlev_(0L). Accordingly, the high frequency amplification gain of the CTLE 1100 may be fine-tuned by a more precise signal EQ_AC[N_(AC)-1:0] generated by the controller 1500.

Similarly, the difference dlev_(0HD) obtained from the (j+1)^(th) first training data pattern is smaller than the difference dlev_(0HD) obtained from the j^(th) first training data pattern. Accordingly, the low frequency amplification gain of the CTLE 1100 may be fine-tuned by a more precise signal EQ_DC[N_(DC)-1:0] generated by the controller 1500.

In addition, since the differences dlev_(1D) and dlev_(2D) obtained from the (j+1)^(th) second training data pattern are smaller than the differences dlev_(1D) and dlev_(2D) obtained from the j^(th) second training data pattern, more precise data levels dlev₁ and dlev₂ may be obtained.

As described above, when the PAM4 receiver is trained by repeatedly receiving the same training pattern until the differences dlev_(0LD), dlev_(0HD), dlev_(1D) and dlev_(2D) become zero or converge to zero, the PAM4 signal received during the actual use of the PAM4 receiver may be precisely determined despite the attenuation of the transmission line.

The PAM4 receiver and the method for training the same according to the present invention has the following advantages.

(1) The PAM4 receiver and the method for training the same according to the present invention are advantageous in that accurate data reception is achieved by adaptively tuning the PAM4 receiver using the training pattern.

(2) The PAM4 receiver and the method for training the same according to the present invention are advantageous in that long-distance, high-speed communication may be achieved. 

1. A PAM4 (pulse amplitude modulation 4) receiver comprising: a CTLE (continuous-time linear equalizer) receiving a signal containing: (i) a first training data pattern containing data “00” and consecutively arranged first data “11” through m^(th data “)11”; and (ii) a second training data pattern including one of data “01”, data “10” and combinations thereof, and equalizing the signal according to an equalization parameter of the CTLE including a high frequency amplification gain and a low frequency amplification gain, and outputting a signal CTLE_out containing equalized first training data pattern and equalized second training data pattern; a sampler sampling: (i) a difference dlev_(3HD); (ii) a difference dlev_(3LD); and (iii) a difference dlev_(1D) or dlev_(2D), and outputting sampled differences as a signal SAMPLE_out, wherein the difference dlev_(3HD) is a difference between: a first voltage level of the signal CTLE_out corresponding to the first data “11” of the equalized first training data pattern when a transition from the data “00” to the first data “11” occurs; and an upper limit dlev_(3H), the difference dlev_(3LD) is a difference between: a second voltage level of the signal CTLE_out corresponding to one of second data “11” through the m^(th data “)11” of the equalized first training data pattern; and a lower limit dlev_(3L), the difference dlev_(1D) is a difference between: a third voltage level of the signal CTLE_out corresponding to the data “01” of the equalized second training data pattern; and the data level dlev₁ corresponding to the data “01”, and the difference dlev_(2D) is a difference between: a fourth voltage level of the signal CTLE_out corresponding to the data “10” of the equalized second training data pattern; and the data level dlev2 corresponding to data “10”; a DEMUX (demultiplexer) parallelizing the signal SAMPLE_out, and outputting parallelized signal SAMPLE_out as a signal DATA_out; a CDR (clock-and-data recovery) providing a clock signal for sampling to the sampler and the DEMUX; and a controller: (i) adaptively adjusting a high frequency amplification gain and a low frequency amplification gain of the CTLE by generating and providing a signal EQ_AC[N_(AC)-1:0] and a signal EQ_DC[N_(DC)-1:0] for adjusting the high frequency amplification gain and low frequency amplification gain based on the difference dlev_(3HD) and the difference dlev_(3LD) in the signal DATA_out, respectively; and (ii) providing the sampler with threshold voltages V_(TH01), V_(TH12) and V_(TH23), the data level dlev₁ or dlev₂, and the upper limit dlev_(3H) and the lower limit dlev_(3L), wherein the threshold voltages V_(TH01), V_(TH12) and V_(TH23) are calculated from: a data level dlev₀ corresponding to the data “00”; the data level dlev₁ or dlev₂; and a data level dlev₃ corresponding to the data “11”, the data levels dlev₁ and dlev₂ are determined from the differences dlev_(1D) and dlev_(2D), respectively; and the data level dlev₃ is determined from the upper limit dlev_(3H) and the lower limit dlev_(3L) (where m is a natural number equal to or greater than 2, and N_(AC) and N_(DC) are natural numbers, respectively).
 2. The PAM4 receiver of claim 1, wherein the CTLE comprises: a differential amplifier provided with transistors; N_(AC) capacitors C_(unit) connected between sources of the transistors; and N_(DC) resistors R_(unit) connected between the sources of the transistors, and the controller selectively turns on the N_(AC) capacitors C_(unit) according to the signal EQ_AC[N_(AC)-1:0] to adaptively adjust the high frequency amplification gain, and selectively turns on the N_(DC) resistor R_(unit) according to the signal EQ_DC[N_(DC)-1:0] to adaptively adjust the low frequency amplification gain.
 3. The PAM4 receiver of claim 2, wherein the controller lowers the upper limit dlev_(3H) and the lower limit dlev_(3L) when the first voltage level of the signal CTLE_out is lower than the upper limit dlev_(3H) even with the high frequency amplification gain at maximum by turning on an entirety of the N_(AC) capacitors C_(unit).
 4. The PAM4 receiver of claim 1, wherein the controller: determines the data level dlev₁ or dlev₂ based on a sign of the difference dlev_(1D) or dlev_(2D); and provides the sampler with the threshold voltages V_(TH01), V_(TH12) and V_(TH23) thereof calculated according to equations ${{{dle}v_{3}} = \frac{{dlev_{3H}} + {dlev_{3L}}}{2}},{V_{TH01} = \frac{{dlev_{0}} + {dlev}_{1}}{2}},{V_{TH12} = {{\frac{{dlev_{1}} + {dlev_{2}}}{2}\mspace{14mu}{and}\mspace{14mu} V_{TH23}} = {\frac{{dlev_{2}} + {dlev}_{3}}{2}.}}}$
 5. A PAM4 receiver comprising: a CTLE (continuous-time linear equalizer) receiving a signal containing: (i) a first training data pattern containing data “11” and consecutively arranged first data “00” through m^(th data “)00”; and (ii) a second training data pattern including one of data “01”, data “10” and combinations thereof, and equalizing the signal according to an equalization parameter of the CTLE including a high frequency amplification gain and a low frequency amplification gain, and outputting a signal CTLE_out containing equalized first training data pattern and equalized second training data pattern; a sampler sampling: (i) a difference dlev_(0LD); (ii) a difference dlev_(0HD); and (iii) a difference dlev_(1D) or dlev_(2D), and outputting sampled differences as a signal SAMPLE_out, wherein the difference dlev_(0LD) is a difference between: a first voltage level of the signal CTLE_out corresponding to the first data “00” of the equalized first training data pattern when a transition from the data “11” to the first data “00” occurs; and a lower limit dlev_(0L), the difference dlev_(0HD) is a difference between: a second voltage level of the signal CTLE_out corresponding to one of second data “00” through the m^(th) data “00” of the equalized first training data pattern; and an upper limit dlev_(0H), the difference dlev_(2D) is a difference between: a third voltage level of the signal CTLE_out corresponding to the data “10” of the equalized second training data pattern; and the data level dlev₂ corresponding to the data “10”, and the difference dlev_(1D) is a difference between: a fourth voltage level of the signal CTLE_out corresponding to the data “01” of the equalized second training data pattern; and the data level dlev₁ corresponding to data “01”; a DEMUX (demultiplexer) parallelizing the signal SAMPLE_out, and outputting parallelized signal SAMPLE_out as a signal DATA_out; a CDR (clock-and-data recovery) providing a clock signal for sampling to the sampler and the DEMUX; and a controller: (i) adaptively adjusting a high frequency amplification gain and a low frequency amplification gain of the CTLE by generating and providing a signal EQ_AC[N_(AC)-1:0] and a signal EQ_DC[N_(DC)-1:0] for adjusting the high frequency amplification gain and low frequency amplification gain based on the difference dlev_(0LD) and the difference dlev_(0HD) in the signal DATA_out, respectively; and (ii) providing the sampler with threshold voltages V_(TH01), V_(TH12) and V_(TH23), the data level dlev₁ or dlev₂, and the upper limit dlev_(0H) and the lower limit dlev_(0L), wherein the threshold voltages V_(TH01), V_(TH12) and V_(TH23) are calculated from: a data level dlev₀ corresponding to the data “00”; the data level dlev₁ or dlev₂; and a data level dlev₃ corresponding to the data “11”, the data levels dlev₁ and dlev₂ are determined from the differences dlev_(1D) and dlev_(2D), respectively; and the data level dlev₀ is determined from the lower limit dlev_(0L) and the upper limit dlev_(0H) (where m is a natural number equal to or greater than ₂, and N_(AC) and N_(DC) are natural numbers, respectively).
 6. The PAM4 receiver of claim 5, wherein the CTLE comprises: a differential amplifier provided with transistors; N_(AC) capacitors C_(unit) connected between sources of the transistors; and N_(DC) resistors R_(unit) connected between the sources of the transistors, and the controller selectively turns on the N_(AC) capacitors C_(unit) according to the signal EQ_AC[N_(AC)-1:0] to adaptively adjust the high frequency amplification gain, and selectively turns on the N_(DC) resistor R_(unit) according to the signal EQ_DC[N_(DC)-1:0] to adaptively adjust the low frequency amplification gain.
 7. The PAM4 receiver of claim 6, wherein the controller elevates the upper limit dlev_(0H) and the lower limit dlev_(0L) when the first voltage level of the signal CTLE_out is higher than the lower limit dlev_(0L) even with the high frequency amplification gain at maximum by turning on an entirety of the N_(AC) capacitors C_(unit).
 8. The PAM4 receiver of claim 5, wherein the controller: determines the data level dlev₁ or dlev₂ based on a sign of the difference dlev_(1D) or dlev_(2D); and provides the sampler with the threshold voltages V_(TH01), V_(TH12) and V_(TH23) thereof calculated according to equations ${{dlev}_{0} = \frac{{dlev_{0H}} + {dlev_{0L}}}{2}},{V_{TH01} = \frac{{dlev_{0}} + {dlev}_{1}}{2}},{V_{TH12} = {{\frac{{dlev_{1}} + {dlev_{2}}}{2}\mspace{14mu}{and}\mspace{14mu} V_{TH23}} = {\frac{{dlev_{2}} + {dlev}_{3}}{2}.}}}$
 9. A method of training a PAM4 (pulse amplitude modulation 4) receiver comprising a linear equalizer, a sampler, a DEMUX (demultiplexer) and a controller, the method comprising: (a) receiving a signal containing: (i) a first training data pattern containing data “00” and consecutively arranged first data “11” through m^(th) data “11”; and (ii) a second training data pattern including one of data “01”, data “10” and combinations thereof; (b) equalizing the signal received in step (a) according to an equalization parameter of the CTLE including a high frequency amplification gain and a low frequency amplification gain, and outputting a signal CTLE_out containing equalized first training data pattern and equalized second training data pattern; (c) sampling: (i) a difference dlev_(3HD); (ii) a difference dlev_(3LD)and (iii) a difference dlev_(1D) or dlev_(2D) according to a sampling parameter of the sampler, and outputting sampled differences as a signal SAMPLE_out, wherein the difference dlev_(3HD) is a difference between: a first voltage level of the signal CTLE_out corresponding to the first data “11” of the equalized first training data pattern when a transition from the data “00” to the first data “11” occurs; and an upper limit dlev_(3H), the difference dlev_(3LD) is a difference between: a second voltage level of the signal CTLE_out corresponding to one of second data “11” through the m^(th data “)11” of the equalized first training data pattern; and a lower limit dlev_(3L), the difference dlev_(1D) is a difference between: a third voltage level of the signal CTLE_out corresponding to the data “01” of the equalized second training data pattern; and the data level dlev₁ corresponding to the data “01”, and the difference dlev_(2D) is a difference between: a fourth voltage level of the signal CTLE_out corresponding to the data “10” of the equalized second training data pattern; and the data level dlev₂ corresponding to data “10”; (d) parallelizing the signal SAMPLE_out, and outputting parallelized signal SAMPLE_out as a signal DATA_out; (e) generating a signal EQ_AC[N_(AC)-1:0] and a signal EQ_DC[N_(DC)-1:0] for adjusting the high frequency amplification gain and low frequency amplification gain based on the difference dlev_(3HD) and the difference dlev_(3LD) in the signal DATA_out, respectively; (f) generating threshold voltages V_(TH01), V_(TH12) and V_(TH23) of the sampler by calculating the threshold voltages V_(TH01), V_(TH12) and V_(TH23) from: a data level dlev₀ corresponding to the data “00”; the data level dlev₁ or dlev₂; and a data level dlev₃ corresponding to the data “11”, wherein the data level dlev₁ or dlev₂ is determined from the difference dlev_(1D) or dlev_(2D), respectively, and the data level dlev₃ is determined from the upper limit dlev_(3H) and the lower limit dlev_(3L); (g) adaptively adjusting the equalization parameter including the high frequency amplification gain and low frequency amplification using the signal EQ_AC[N_(AC)-1:0] and signal EQ_DC[N_(DC)-1:0] generated in step (e); and (h) adaptively adjusting the sampling parameter of the sampler according to the threshold voltages V_(TH01), V_(TH12) and V_(TH23), the data level dlev₁ or dlev₂, and the upper limit dlev_(3H) and the lower limit dlev_(3L) generated in step (f) (where m is a natural number equal to or greater than 2, and N_(AC) and N_(DC) are natural numbers, respectively).
 10. The method of claim 9, further comprising: performing step (a) through step (d) after performing step (a) through step (h) based on the equalization parameter and the sampling parameter adaptively adjusted in step (g) and step (h), respectively.
 11. The method of claim 9, wherein step (f) comprises: (f-1) determining the data level dlev₁ or dlev₂ based on a sign of the difference dlev_(1D) or dlev_(2D); and (f-2) calculating the threshold voltages V_(TH01), V_(TH12) and V_(TH23) according to equations ${{dlev}_{3} = \frac{{dlev_{3H}} + {dlev_{3L}}}{2}},{V_{{TH}\; 01} = \frac{{dlev_{0}} + {dlev_{1}}}{2}},{V_{TH12} = {{\frac{{dlev_{1}} + {dlev_{2}}}{2}\mspace{14mu}{and}\mspace{14mu} V_{{TH}\; 23}} = {\frac{{dlev_{2}} + {dlev}_{3}}{2}.}}}$
 12. The method of claim 9, wherein step (g) comprises: (g-1) selectively turning on N_(AC) capacitors C_(unit) provided in the CTLE according to the signal EQ_AC[N_(AC)-1:0] to adaptively adjust the high frequency amplification gain; and (g-2) selectively turning on N_(DC) resistor R_(unit) provided in the CTLE according to the signal EQ_DC[N_(DC)-1:0] to adaptively adjust the low frequency amplification gain.
 13. The method of claim 12, wherein step (g) further comprises: (g-3) lowering the upper limit dlev_(3H) and the lower limit dlev_(3L) when the first voltage level of the signal CTLE_out is lower than the upper limit dlev_(3H) even with the high frequency amplification gain at maximum by turning on an entirety of the N_(AC) capacitors C_(unit).
 14. A method of training a PAM4 (pulse amplitude modulation 4) receiver comprising a CTLE (continuous-time linear equalizer), a sampler, a DEMUX and a controller, the method comprising: (a) receiving a signal containing: (i) a first training data pattern containing data “11” and consecutively arranged first data “00” through m^(th data “)00”; and (ii) a second training data pattern including one of data “01”, data “10” and combinations thereof; (b) equalizing the signal received in step (a) according to an equalization parameter of the CTLE including a high frequency amplification gain and a low frequency amplification gain, and outputting a signal CTLE_out containing equalized first training data pattern and equalized second training data pattern; (c) sampling: (i) a difference dlev_(0LD); (ii) a difference dlev_(0HD); and (iii) a difference dlev_(1D) or dlev_(2D) according to a sampling parameter of the sampler, and outputting sampled differences as a signal SAMPLE_out, wherein the difference dlev_(0LD) is a difference between: a first voltage level of the signal CTLE_out corresponding to the first data “00” of the equalized first training data pattern when a transition from the data “11” to the first data “00” occurs; and a lower limit dlev_(0L), the difference dlev_(0HD) is a difference between: a second voltage level of the signal CTLE_out corresponding to one of second data “00” through the m^(th) data “00” of the equalized first training data pattern; and an upper limit dlev_(0H), the difference dlev_(2D) is a difference between: a third voltage level of the signal CTLE_out corresponding to the data “10” of the equalized second training data pattern; and the data level dlev₂ corresponding to the data “10”, and the difference dlev_(1D) is a difference between: a fourth voltage level of the signal CTLE_out corresponding to the data “01” of the equalized second training data pattern; and the data level dlev₁ corresponding to data “01”; (d) parallelizing the signal SAMPLE_out, and outputting parallelized signal SAMPLE_out as a signal DATA_out; (e) generating a signal EQ_AC[N_(AC)-1:0] and a signal EQ_DC[N_(DC)-1:0] for adjusting the high frequency amplification gain and low frequency amplification gain based on the difference dlev_(0LD) and the difference dlev_(0HD) in the signal DATA_out, respectively; (f) generating threshold voltages V_(TH01), V_(TH12) and V_(TH23) of the sampler by calculating the threshold voltages V_(TH01), V_(TH12) and V_(TH23) from: a data level dlev₀ corresponding to the data “00”; the data level dlev₁ or dlev₂; and a data level dlev₃ corresponding to the data “11”, wherein the data level dlev₁ or dlev₂ is determined from the difference dlev_(1D) or dlev_(2D), respectively, and the data level dlev₀ is determined from the lower limit dlev_(0L) and the upper limit dlev_(0H); (g) adaptively adjusting the equalization parameter including the high frequency amplification gain and low frequency amplification using the signal EQ_AC[N_(AC)-1:0] and signal EQ_DC[N_(DC)-1:0] generated in step (e); and (h) adaptively adjusting the sampling parameter of the sampler according to the threshold voltages V_(TH01), V_(TH12) and V_(TH23), the data level dlev₁ or dlev₂, and the lower limit dlev_(0L) and the upper limit dlev_(0H) generated in step (f) (where m is a natural number equal to or greater than 2, and N_(AC) and N_(DC) are natural numbers, respectively).
 15. The method of claim 14, further comprising: performing step (a) through step (d) after performing step (a) through step (h) based on the equalization parameter and the sampling parameter adaptively adjusted in step (g) and step (h), respectively.
 16. The method of claim 14, wherein step (f) comprises: (f-1) determining the data level dlev₁ or dlev₂ based on a sign of the difference dlev_(1D) or dlev_(2D), respectively, and (f-2) calculating the threshold voltages V_(TH01), V_(TH12) and V_(TH23) according to equations ${{dlev_{0}} = \frac{{dlev_{0H}} + {dlev_{0L}}}{2}},{V_{{TH}\; 01} = \frac{{dlev_{0}} + {{dle}v_{1}}}{2}},{V_{{TH}\; 12} = {{\frac{{dlev_{1}} + {dlev_{2}}}{2}\mspace{14mu}{and}\mspace{14mu} V_{{TH}\; 23}} = {\frac{{dlev_{2}} + {dlev}_{3}}{2}.}}}$
 17. The method of claim 14, wherein step (g) comprises: (g-1) selectively turning on N_(AC) capacitors C_(unit) provided in the CTLE according to the signal EQ_AC[N_(AC)-1:0] to adaptively adjust the high frequency amplification gain; and (g-2) selectively turning on N_(DC) resistor R_(unit) provided in the CTLE according to the signal EQ_DC[N_(DC)-1:0] to adaptively adjust the low frequency amplification gain.
 18. The method of claim 17, wherein step (g) further comprises: (g-3) elevating the lower limit dlev_(0L) and the upper limit dlev_(0H) when the first voltage level of the signal CTLE_out is higher than the lower limit dlev_(0L) even with the high frequency amplification gain at maximum by turning on an entirety of the N_(AC) capacitors C_(unit). 